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Discussion Starter #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:
 

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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.
 

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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.
 

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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.
 

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Discussion Starter #7 (Edited)
Check your MAF sensor.
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...
 

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Discussion Starter #9 (Edited)
Stalling a lot? Hows your fuel pressure?
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
 

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Discussion Starter #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?
 

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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=&
 

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Discussion Starter #13
Its probably worth a shot. Worse case scenario is it doesn't fix it.
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?
 

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Discussion Starter #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?
 

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Discussion Starter #16
Alright I'm getting confused now. Sorry to be a ****, but repeat whats going on with your car starting from problem one, if you don't mind.
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...
 

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Just out of curiousity , did you pull any codes ?
 

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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.
 

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Same Here

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.
 

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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?
 
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