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86 TPI Idles Rough, Surges, and Stalls?

66K views 77 replies 13 participants last post by  konadale 
#1 ·
Hi, Im new to the Forum, this is my second post :seeya:

I recently bought an 86E TPI and its got an interesting set of issues, especially with idle. Id like some opinions and input to start planning a repair route please. Its got a freshly rebuilt motor and trans, AIR pump delete, EGR is connected directly to the plenum(that right?), some hoses are plugged with blots and screws(dislike), its less than perfect :) I want to fix and restore it, versus watch it rot away.

On start up, the idle drops to 400/500RPM then goes up to 1200RPM, then the idle lowers to and alternates between 600 and 900 RPM. It never stays constant. Its stalling under a minute after start up, and it will stall once the idle drops if I rev it while its in P. Also stalls sometimes when shifting into gear(from R to D). I tried changing out the fuel pump with a new one, but then it would not start. I changed the plugs and wires but to no avail. Any help would be appreciated! This car has potential and Im more a body man than I mechanic, but I love wrenching and getting dirty so Im not afraid to get into it! Want this C4 to actually look and run smoothly like I believe a Vette should :thumbsup3:
 
#7 · (Edited)
That was my first thought. :thumbsup3:
I has a brand new MAF sensor. Ill try cleaning it with MAF Cleaner...

My first thought is not your MAF sensor. Rather than going out and spending even more money on something that may or may not work. Your time would better be spent cleaning up your vac lines.
I'm willing to bet that is where your problem lies.
I will replace them and get back to you on that :)

Idel Air Control Vavle (IACV).

Also Chech the Pink Wire next to the Fire wall next to the distributor you have look stright down between the firewall and the motor to see it, This wire for the spark Advance or anti knock box on the passside by the Heater fan.

I broke mine during the motor swap the pink wire I also had a IACV go bad on me all these cause the problems you are having after you check for vacume leaks.
I try to look for this pink wire after work... Oh, this Corvette has no heater or A/C unit and lines. Have an 85 parts car I will be taking the parts from to install it onto my 86. I will order a new IAC soon. Maybe an EGR valve at the same time?

I agree with Marv02, an Idle Air Control valve is a possibility.

I would agree with Slvrvette only if the OP's condition got progressively worse. If it just one day started running like garbage, that sounds more like a faulty component, unless of course a vac line got disconnected.

Either way all are good suggestions; be sure to give your car a thorough diagnosis and as was stated by others, don't just throw your money away at what you think is wrong.
Corvette had this problem when I purchased it 2 months ago. BUT, it has gotten worse with the addition of stalling after revving, stalling after starting, and stalling twice while I was at stop lights in the city...
 
#4 ·
My first thought is not your MAF sensor. Rather than going out and spending even more money on something that may or may not work. Your time would better be spent cleaning up your vac lines.
I'm willing to bet that is where your problem lies.
 
#5 · (Edited)
Idel Air Control Vavle (IACV).

Also Chech the Pink Wire next to the Fire wall next to the distributor you have look stright down between the firewall and the motor to see it, This wire for the spark Advance or anti knock box on the passside by the Heater fan.

I broke mine during the motor swap the pink wire I also had a IACV go bad on me all these cause the problems you are having after you check for vacume leaks.
 
#6 ·
I agree with Marv02, an Idle Air Control valve is a possibility.

I would agree with Slvrvette only if the OP's condition got progressively worse. If it just one day started running like garbage, that sounds more like a faulty component, unless of course a vac line got disconnected.

Either way all are good suggestions; be sure to give your car a thorough diagnosis and as was stated by others, don't just throw your money away at what you think is wrong.
 
#9 · (Edited)
I'll check it with a fuel pressure gauge and report back. It stalled on me twice while I was driving in the city one day shortly after I bought it. Also stalled twice when I shifted from R to D in a parking lot. I inspected my fuel pump and saw debris in the strainer so I tried changing out the fuel pump, but that only led to a no start situation. I had fuel at the injectors, but no fire. Put the old pump back in and it started up with some effort... I was listening to the idle today(it wasn't stalling under a minute after start up anymore), I noticed that when the idle drops, so does the tone of the fuel pump noise. Wrong pump maybe? The plastic connector tip on the wiring harness matched up though...

Edit: Fuel pressure is at 39/40PSI
 
#10 ·
This car has an EGR Valve but no EGR Solenoid... Read on Ecklers a faulty/broken EGR solenoid causes rough idle and stalling... Should I look into this is well? I have an EGR sol. from an 85 Corvette if that would work?
 
#13 ·
Alright. At least I'll have a new solenoid for the Vette.

I am using a EGR vale off a newwer Vet I had to change out the pig tail and use a Vacume T on one of the ports and rebend the mounting bracket to get it to work.

But theres some china brands out there now that just bolt on.

Try this link:
http://www.zip-corvette.com/ProductDetails/ProductDetails.aspx?pid={2d04e543-4326-44f1-8002-e4dc92f8ec70}&gid={09139179-da03-4d31-875a-ee619e22068f}&GroupName=EGR+Valves&pname=85-90+EGR+Control+Valve+Relay+Solenoid&Referer=&Alias=&ptct=GL1-SR&CTitle=&
That's what I was looking at last night lol Im assuming yours works okay?
 
#12 ·
I am using a EGR vale off a newwer Vet I had to change out the pig tail and use a Vacume T on one of the ports and rebend the mounting bracket to get it to work.

But theres some china brands out there now that just bolt on.

Try this link:
http://www.zip-corvette.com/ProductDetails/ProductDetails.aspx?pid={2d04e543-4326-44f1-8002-e4dc92f8ec70}&gid={09139179-da03-4d31-875a-ee619e22068f}&GroupName=EGR+Valves&pname=85-90+EGR+Control+Valve+Relay+Solenoid&Referer=&Alias=&ptct=GL1-SR&CTitle=&
 
#14 · (Edited)
Okay, and now my Vette is parked at work my workplace because it won't start... :doh: Geez this car. General Malfunction is a perfect summary of it right now lol Perhaps my previous issues were. Symptom of a true problem... Gonna check to see if im getting spark and fuel again.

Edit: Looks like engine is being flooded with fuel... Getting air and good spark, a bad fuel pressure regulator maybe?
 
#16 ·
lol Don't see any implication of you being one Seabee :)

Alright, when I first bought it, it had a problem with idle and it stalled a couple times.

The Low Coolant Sensor was also just hanging in the engine bay. I read that it was tied to idle from 84-89 as a failsafe to prevent the car from overheating. I grounded that wire and idle improved, but just slightly.

Checked the plugs and found them tipped off with oil(typical of a rebuilt engine), so I replaced the spark plugs and wires just to get it out of the way. I don't trust anything of the previous owner. Again, the idle improved, but only slightly.

Now, just this week it started stalling within 1 minute after start up, in addition to the idle issue. I assumed it was a fuel problem or something to do with the intake because I know I'm getting good spark. I noticed while listening to the fuel pump that when my idle drops, so does the sound of the fuel pump. I tested my fuel pressure as suggested, and I was getting 39/40PSI at the rail. I tried changing out my fuel pump to a new one, but then it wouldn't start... :confused: Reinstalled old fuel pump and it started with a little effort.

Went to work yesterday, car was fine. Finished work, time to go home. I turned the key forward and there was a loud vibration and noise coming from the back of the car(in or around the fuel tank) and the Vette wouldn't start... ???? Just so happens earlier that morning, I bought a new fuel filter, so I replaced that in a few minutes and tried to start it again. Better results, car wants to start, but still no go... I don't understand...
 
#17 ·
Just out of curiousity , did you pull any codes ?
 
#21 · (Edited)
Got the car to start. That tiny metal and plastic piece that connects the in-tank fuel line to the fuel pump came loose. Reconnected it and car starts now. Idle is still the same so Im back to where I started. Took the Vette out to the track to check its performance, ran a 14.791 @ 95MPH on a .114RT in OD gear. Not far off the 14.4 I read it could do brand new.Went home right after So performance isnt affected as much as I thought it would be. Just had to keep my foot lightly on the throttle to keep the idle at 850RPM in line up. Its fine while driving, but just terrible at idle :coffeetime: Its odd lol



This for the ALDL connector? How do I check for codes? I don't have access to OBD scanners...

Was your replacement fuel pump a re-manufactured one or brand new? Re-man parts suck you may have gotten a spanked fuel pump.

Also, stupid as it sounds, are you 100% sure you installed the replacement fuel pump correctly? No crossed or disconnected wires?

The way you said you had a vibrating noise coming from the fuel tank only leads me to believe your fuel pump, though may not be the problem, is giving you issues.
The pump was purchased brand new(or so I think). Sales didnt mention anything about it being a re-manufactured or refurbished part. Yes, I did it correctly. I changed it out again just for the hell of it and same results. Old pump works, 'new' one doesn't.

Man sounds alot like what I;m fighting.except I think I'm hearing my EGR sucking air badly.but it has all of you symptons.Ive checked all my vac hose's still no luck.
Well good luck. This situation is quite interesting so far lol But Im getting more help here than from local mechanics. Half of them are afraid to touch it because its FI, and the other half because its a Corvette. Im the only C4 Corvette in my area that I know of lol :patriot:
 
#18 ·
Was your replacement fuel pump a re-manufactured one or brand new? Re-man parts suck you may have gotten a spanked fuel pump.

Also, stupid as it sounds, are you 100% sure you installed the replacement fuel pump correctly? No crossed or disconnected wires?

The way you said you had a vibrating noise coming from the fuel tank only leads me to believe your fuel pump, though may not be the problem, is giving you issues.
 
#20 ·
Alright back to the basics first before you replace anything else.
Spark is good
Fuel pressure is good
TPS set to .545 volts?

I'm understanding your CTS is just hanging there?
Have you followed a diagram of ALL your vac lines and they are correct?
 
#22 · (Edited)
Improvement!

Just off a hunch... I took the TB off my black 85 and inspected it... Took off the TPS and compared it to my current unit on my 86. It looked cleaner than my current one, so I swapped both and fiddled with the TPS positioning and the minimum idle screw and what do you know? The idle is better. Its not great, but still an improvement over what it was. Idle stays between 790-860RPM now and not 5XX-900 lol I also took out my IAC Valve and sprayed it with carb cleaner(it was a little dirty lol).

Just to know, what are your guys' typical idle RPMs?? So I know what to generally shoot for?
 
#24 ·
Alright, went and learned how. TPS Voltage is set to .545 Volts. Idle seemed better so I went and took it for a short spin. Didn't surge when shifting into gear :) Came home and shifted into P, then the idle speed increased to 1300RPM... Adjusted the minimum idle screw and was able to bring it down to 970RPM but thats all the play I could get... Turned it off to get ready for work. It started with an RPM of 380-500RPM the dies... Tried starting at again, this time it starts then stalls. I can't wait for that new fuel pump! :coffeetime:
 
#25 · (Edited)
Your engine should be able to idle in NEUTRAL at 700 rpm or less. I suspect your throttle body isn't adjusted right and is the reason you have such a high idle speed. The butterflies should be adjusted to the point where they are almost sticking in their bores and then the IAC will provide the needed air. So I suggest backing out the adjustment screw until the butterflies DO stick then turn it in just far enough to where they don't stick. To adjust it you can slip a .0015" feeler gauge between the bore and trailing edge of the butterfly then back the adjustment screw out until the feeler gauge gets snug. Then check your TPS voltage again and adjust it if necessary.
 
#28 · (Edited)
Installed new fuel pump and relay. Car started!

I bought a digital multimeter yesterday to use for electrical testing.

What is my CTS?(hanging?)
 
#30 ·
CTS is coolant temperture sensor, you had mention it was just hanging there.
In order to get the correct fueling to the injectors you HAVE TO HAVE the oxygen senors and CTS in place. Without those you might just well throw a carb on it because it will not run correctly...:thumbsup3:
 
#33 ·
Not yet. I have an appointment for next week when my exhaust guy gets a free moment. I have no O2 sensor ports anywhere on my exhaust system set up. I think I'll also need to purchase or find O2 sensor bungs for my set up. I purchased 1 O2 sensor because I could only find 1 wiring harness, but to me that doesnt make sense... Arent there supposed to be at least 2? (before and after the cat).

My current exhaust set up is as follows:
Hedman LT Headers
Dual H Pipe with 2 Magnaflow cats
Borla ProXS Mufflers w/ polished SS LT1 tips

I added the Borla mufflers and tips.
 
#34 ·
O2 Sensors

You might be able to make your own bung using a short piece of pipe and the correct metric tap. As far as I know the O2 sensor(s) are always ahead of the catalytic converter. My '82 uses only one and it's about 3" ahead of the converter but later models used two and they're both screwed into the exhaust pipes real close to the exhaust manifolds so the computer can read temperatures from both sides of the engine.
 
#38 ·
You might be able to make your own bung using a short piece of pipe and the correct metric tap. As far as I know the O2 sensor(s) are always ahead of the catalytic converter. My '82 uses only one and it's about 3" ahead of the converter but later models used two and they're both screwed into the exhaust pipes real close to the exhaust manifolds so the computer can read temperatures from both sides of the engine.
I already ordered O2 bungs a week ago. But I can use whatever is left over for my other car or project :thumbsup3:

The IAC is located on the throttle body, and it is mostly responsible for how the car idles. You can usually tell if it's working because it'll add idle and compensate for the load the AC compressor adds when it comes on, but since you don't have AC, you can't use that indication. I've read somewhere that you can test the IAC, but I've tested them before, and they seem fine, but when I replaced them, the idle issues went away, so testing doesn't always prove them as good. Symptoms were the same as yours, stalling, rough idle, had to hold foot on the gas, etc. I highly recommend replacing it. They're 50-70 dollars.
How often have you changed out your IAC? I will change mine soon. It's $100 for me. Lucky for me I live across the Pacific :patriot:

I believe you can test them by just turning the key on. I think the pintle retracts all the way when the key is turned on and then when the engine starts it screws in to limit the amount of air going through it. On my '82 I can see them (the CrossFires have two) move whenever I make any kind of throttle change.
I will try that lol

The IAC motors have brushes in them so they will only last as long as their brushes last. They are known as "stepper" motors as they will run both directions as the computer reverses the motor's polarity. My '82's original IAC's lasted 200,000 miles.
I have an extra IAC from my 85 and the two seem different. The pintle on my 86s wiggles if I touch it and the spring isn't straight. The pintle on my 85s is solid and doesn't move, and its spring has way more coils than my 86's.
 
#35 ·
IAC valve controls alot of the idle

The IAC is located on the throttle body, and it is mostly responsible for how the car idles. You can usually tell if it's working because it'll add idle and compensate for the load the AC compressor adds when it comes on, but since you don't have AC, you can't use that indication. I've read somewhere that you can test the IAC, but I've tested them before, and they seem fine, but when I replaced them, the idle issues went away, so testing doesn't always prove them as good. Symptoms were the same as yours, stalling, rough idle, had to hold foot on the gas, etc. I highly recommend replacing it. They're 50-70 dollars.
 
#36 ·
The IAC is located on the throttle body, and it is mostly responsible for how the car idles. You can usually tell if it's working because it'll add idle and compensate for the load the AC compressor adds when it comes on, but since you don't have AC, you can't use that indication. I've read somewhere that you can test the IAC, but I've tested them before, and they seem fine, but when I replaced them, the idle issues went away, so testing doesn't always prove them as good. Symptoms were the same as yours, stalling, rough idle, had to hold foot on the gas, etc. I highly recommend replacing it. They're 50-70 dollars.

I believe you can test them by just turning the key on. I think the pintle retracts all the way when the key is turned on and then when the engine starts it screws in to limit the amount of air going through it. On my '82 I can see them (the CrossFires have two) move whenever I make any kind of throttle change.
 
#39 ·
Did you have any progress yet? Curious to see how this turns out.

On a side note, I know you have an actual distributor, but I learned something about my 94 Corvette with LT1 and optispark.
Even if it is off by ONE spline, it will surge and stall and act all kind of stupid, like as if it's the IAC or too much fuel. It seemed to perform ok, but it wouldn't idle right or run very smooth even at low throttle opening, which made me decide to look at something other than the IAC. I'd just put on new wires, TR55 plugs, and an MSD cap and rotor, but had to remove the whole distributor in order to get the dang screws out of the old rotor with a T9 Torx bit (which by the way I found at Autozone in a set of T9- T6, for 10 bucks, they just started carrying them). SO when I reinstalled it, I managed to misalign the rotor and the shaft from the cam gear and it was advanced. One thing that tipped me off was that when I accelerated, it rattled like detonation, so I went back into the optispark, and sure enough, it was off one stinking spline. Lined it back up, and VOILA! Purrs like a kitten now.
Now, I know you've got a distributor, but you still have a lot of computer control, so maybe check your timing. Could be off enough that the computer can't compensate for it and is causing all your issues.
 
#40 ·
Actually I think this is right on the money. I know for a fact my Vette is running rich. Like, really rich. The smell is overpowering to say the least. I already put in a call to my local shop to have the timing checked out. Was supposed to be checked out this past saturday but something came up and so that didnt happen... But it will be done this week, or Im changing shops! Ive been waiting quite a while already. I just want it running right! Plus, I finished all my body work and sanding prep on it so its almost ready for paint! :thumbsup3:
 
#42 · (Edited)
Got a timing light from a friend and checked my timing. Adjusted it 'Upwards' toward the #6 position and reset the computer as it says in my manual. Runs A LOT better! Idle drops a bit for just a second after about 1 minute or 2 of idling, and it still sounds like a slight misfire while driving around town or on the highway every so often, but its way better and it pulls much harder on acceleration. I still haven't gotten around to installing an O2 sensor yet, but will do that soon :)
 
#43 ·
And now Im getting codes 33 and 42... I think I might need to order a jet engine with the next online purchase I make lol Its just one problem after another...
 
#44 ·
Welcome to the world of the C4s.
 
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