98 DX 5 speed 220k all stock

I've noticed on my commute (75 miles) & consistent traffic under 25mph for miles with ambient temp over 120 degrees. My car will high idle over 1200rpm sometimes near 2200 rpms. This is from a normal 650-700 warm idle with IAT below 90 degrees.

I decided to remove the IAC valve completely from the throttle body to clean it. There was a little carbon, not the worst I have scene. I cleaned it with carb cleaner.

I put everything back togeter & now I have the immediate high idle from a cold start up (1200 up to 2800 rpm) and then it surges back and forth from 1200 to 2500 rpm's.

All I did was remove the IAC and clean it. I double checked all plugs & checked for vacuum leaks.

 

if you cleaned your IAC, i would also clean your throttle body if i was at it.

you should do the idle learn procedure:
Check, and if necessary, set your base idle to factory (650 i beleve). then reset your ECU by disconnecting your battery for 10+ mins. then start the car after siting overnight, AKA cold engine, and let idle till radiator fan comes on 3 times.

 

Entire throttle body was removed & cleaned just as the IAV was removed and cleaned in carb cleaner with wire brush assortment. both were shot dry with compressed air. all gaskets were removed prior to cleaning. everything went together quite well.

Meanwhile the battery negative was disconnected. I reconnected everything and was left with a high idle 3000+
that would die down to 1200 and then surge from 1200 to 2800.

I let the car **** for a few minutes and then drove it 5 miles with no change.

I will disconnect the battery tmrw and try your cold idle learn.

-Kevin

 

CEL codes?

Is the throttle cable adjusted too tightly, holding the plate slightly open?

If you cover the top of the TB with the palm of your hand with the engine idling, does the engine die or keep running?

 

Also, did you replace all gaskets, or re-use them?

 

No Codes.

the cable has not been adjusted, I simply removed it and reinstalled it.

hand over the t/b will cause the engine to stall.

I tried your idle re-learn which was bogus.

I will re clean the throttle body and IAC valve tomorrow as well as switch the MAP sensor with a known good one.

 

Does CEL work?

^Does not answer question. Is it too tight or is there slack in it?

Remove intake. With engine high idling, use finger to cover hole inside TB leading to IACV. Does idle speed drop low?

Nothing I do or recommend is bogus.

 

You also rather conveniently skipped over my question.

 

re-used the gaskets, no vacuum leaks confirmed.

CEL works no codes as of yet.

thoroughly cleaning the IAC today I will report back later.

 

let the IAC soak and scrubbed it with a wire brush, it now moves freely





there was quite a bit of rust on the iac coil, I cleaned the rust off -- this may have been a part of the original problem





throttle body got a good cleaning as well

 

Happy to say I put everything back together & the car has never ran this smooth.

I did not have to do an idle learn procedure (is there any literature on this?)

The throttle cable did not need adjustment & the idle was spot on.

Besides the valve itself having carbon buildup, I believe the rust on the magnet was a culprit here.

When cleaning the IAC valve I would highly suggest removing the magnet & cleaning that with emery cloth as well.

 

OP was referring to statement above yours.