Idle issue warm engine

[Heyblue]

1984 Start cold idles good but high 1400. Drive around town then try to start warm engine. SOMETIMES starts but will not idle. I give a little throttle for a few seconds then see if it will idle, usually after a few of these actions it idles fine until I shut down and restart. Again it does not do this every time (except the fast idle at cold, that is a given).
Not sure if it is related, but when starting, I have to crank for longer than I would expect. Especially cold, but even hot it seems to have to turnover a number of times before starting.

 

[G Winter]

you could have bad injectors. Bad temp sensor , not the gauge sensor, can cause warm idle issues. Throttle position sensor could also be a problem. You need to get the codes pulled on it,that might help.

 

[Heyblue]

Thanks for reply; I did a code dump and only get code 12 i.e. no problems detected.
To clarify my problem. Engine is up to temp. and whenever I stop at traffic lights etc it idles fine. I park to run into a store, come back and start the engine. It always starts right up, but SOMETIMES, it will not idle. If that is the case I restart and give it a little throttle then let off. After a few (2 or 3) times it then idles fine for the rest of the time driving. Starting cold it always idles fine except a little high (about 1400RPM) until warmed up.

 

[hcbph]

I had a problem somewhat similar with my 86 after purchase. It would idle high (1400 rpms or better) most of the time and occasionally but rarely drop to normal. Other times when it was cold outside, it would run fine for maybe 5-8 blocks then suddenly barely run at low speed. Shut it off and let it set for 5 minutes and restart and it ran fine. I occasionally would get a SES with a code 42 IIRC.

I chased this for a long time and kept coming back to the TPS or IAC valve as the possible root cause. One day while checking I happened to have a plastic faced hammer and lightly hand rapped the IAC with it a couple of times (engine off at the time). My idle suddenly continually smoothed out and settled down to maybe 700 at idle and has not reoccurred since. I suspect it was the IAC value and plan to eventually replace the valve but for now it's still working just fine for me and lets me drive it for now.

Hope that helps if it's the same problem happens to be yours also.