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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:
 
#47 ·
Would it be wise to replace the MAF sensor burn off relay first? Before I jump into a new MAF sensor.
 
#49 ·
My manual shows a code of MAP, but I do have a MAF unit... Have I made a mistake in part description?
 
#50 ·
I took out and cleaned my MAF and connectors with sensor cleaner... Reset my computer and its not throwing code 33 anymore. Just code 42
 
#52 ·
Code 42 is E.S.T
When you went thru your timing I assume you disconnected the wire?... this will give you the code until you plug it back in. I would check that connector. If the connection is not a good one you will get the code
 
#53 ·
Yes. Car was off, I unplugged that wire connector. Turned car on, shot timing, adjusted to 6 degrees, rechecked TPS at .545 volts, checked out ok, turned car off, reconnected wire, disconnected battery for 1 minute. Did I miss another wire or connector?
 
#55 ·
Testing EST Connection

To test your EST connection your timing should advance up to about 15-16 degrees when you plug the EST connection back together. If your timing doesn't advance then I suspect you have a bad module causing that code to set. If it's the original module and your engine has a lot of miles on it I suggest changing the module based on mileage alone. They don't last forever you know.
 
#57 ·
Sounds like you did disconnect the right wire. TBTR makes a good point in regards to plugging it in and seeing if your timing advances.
FYI- I use white out my timing tabs and the mark for 6 degrees BTDC, makes it real easy when using a timing light.

I don't think its your ESC module, that would be a code 43
 
#58 ·
Alright so... Disconnected battery, reconnected it, unplugged timing bypass wire, started car, timing read at 6 degrees but notices it skips up to 7 degrees sometimes too. Plugged wire back in while car is still running, timing holds steady at 6 degrees. Idle is still loping. Turn off car. Start at up and timing is advanced quite a ways up there. Unplug wire while car is running, idle drops, as does timing. Timing is at 6 degrees. Computer is no longer throwing any codes.
 
#61 · (Edited)
Started this morning, idle was super low, 380-480RPM, took about 15 seconds for idle to increase to normal 600-900 RPM range. Installed new cap, rotor, coil, and ignition module. Car starts faster(didn't want to start after I got home from the store. Started, then died out immediately. ????), but seems idle is very poor on cold starts, is a little better after being warmed up. Once going, everything is fine aside from the same loping idle and what I swear is a random misfire at any given speed.that I just cant seem to figure out. Also still a slight hesitation from when flooring the pedal to the butt dyno feeling any feedback. Not sure if that's a symptom? So that leaves me to check the IAC valve, MAF sensor, and O2 sensor... And perhaps a defective ECM as a last resort.

On a GOOD day, my idle is usually in a pattern like below:
---------____--------------------------------____--------
It will go from a nice 780RPM, drop to 590-640RPM, slowly work its way back up to 730RPM, then top off at 780RPM again for a minute, then repeat.
 
#65 ·
I believe 85-89 all use the 165 ecm. As long as it was use with the same type of transmission as yours.
Autoparts stores do sell the ecm's for around $80
 
#67 ·
Will be painting my Corvette either tomorrow or Monday. I will replace the computer after its finished.
 
#69 ·
Hey guys i just followed the thread and i cant help but throw this in there...

I have an '85 myself and it has its own set of problems similar to this....

-the idle will not remain steady or evn close to it. (400-1600) in p/n
- there is a check engine light but wen i pull codes it reads 12.... So idk to make of that
- under heavy acceleration i can head a very audible squeal like a belt or pully sliping...
- there is smoke and a trans leak (doubt is related to other symptoms)
- digital instrumentation acts up occationaly
- where the taletall switches are (mpg, coolant temp, oil pres. Switches) if i leave it on "coolant temp" it switches back to voltage and that switch by itself has no "off" position it reads voltage in that position.
 
#72 ·
Just a thought are you running full lenght headers if so I had to go with a heated O2 Sending unit.
 
#74 ·
Update: Installed the O2 Sensor. No changes. Will get a new EGR Valve on ASAP and report back.
 
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