Help! 1990 Corvette rough idle

[dperreault]

I have 1990 Corvette 5.7L Automatic, 22000 mile, that runs fine when I get on the gas but surges on slow idle and almost seems like it's going to stall. Come to a light or stop sign, I have to put it in neutral or park so the idle will be a little faster to solve the slow idle problem. This only happens when it is warmed up and the slow idle drops to 500 rpms. I replaced the following parts and the problem still exists:
ECM
Coolant temperature sensor
Throttle postition switch
Fuel filter
MAP sensor
Cleaned the throttle body

No codes are present in the ECM. I would appreciate any help you can give me with this problem

It has been suggested I replace the IAC valve. I can't seem to get it out. Any suggestions.

 

[Rob]

Since this isn't related to the ZR-1, I'm going to move this into the C4 Tech forum...

 

[cantdrive55]

Resolution?

I have 1990 Corvette 5.7L Automatic, 22000 mile, that runs fine when I get on the gas but surges on slow idle and almost seems like it's going to stall. Come to a light or stop sign, I have to put it in neutral or park so the idle will be a little faster to solve the slow idle problem. This only happens when it is warmed up and the slow idle drops to 500 rpms. I replaced the following parts and the problem still exists:
ECM
Coolant temperature sensor
Throttle postition switch
Fuel filter
MAP sensor
Cleaned the throttle body

No codes are present in the ECM. I would appreciate any help you can give me with this problem

It has been suggested I replace the IAC valve. I can't seem to get it out. Any suggestions.

Did you Ever get this fixed???

My 90 vette is having the same problem - I got a tune up, cleaned the throttle body, cleaned the fuel injectors, it still runs rough in idle when it warms up

 

[bill5674]

well i`m not a fan of randomly changing parts,but on my 90 i had the same rough idle problem.I changed out the ignition module,cause of a no start condition and cleared up the idle problem.....bill

 

[Dustoff529]

PVC

had this happen to me... was a failed PVC valve! replaced it and back to ground pounding

When I have your wounded

 

[vetteoz]

I put my money on the IAC , have you tried resetting it before replacing?

 

[cantdrive55]

I haven't changed the PVC or the IAC - those are my next steps. Here is what I have done so far in order of costliness:
1) oil change/air filter
2) cleaned throttle body
3) replaced fuel filter
4) flushed fuel system and injectors
5) full tune up w/ new wires, rotor, distributor

All of you vette owners know how costly it is to "randomly change parts"
The last thing I want to do is throw money away

 

[G Winter]

You may want to check the ohms on the injectors. Should be about 16 ohms. FSM says anything below 10 ohms is replacement time. If any need to be replaced it might be wise to replace all . I found that once one or two fail more are not far behind.

Glenn

 

[vetteoz]

All of you vette owners know how costly it is to "randomly change parts"The last thing I want to do is throw money away

How does it start hot?
PCV easy checked , remove valve , clean and replace.
With it attached to engine and engine running you should feel vac with you finger over end

 

[Ron93ruby]

I had that problem with an 87 and solved it by replacing the IAC.