88 spfi idle fluctuation

[smallwwb]

Once the car is warmed up, the idle goes up and down. I was told by a mechanic that it might be the air control valve. I tried blocking it off and it made no difference.

Can I remove this system? What other faulty emissions stuff can I remove for more reliability/hp/mpg?

:banana:

[dragonfire]

i am having the same problem with a 90 loyale. we poured seafoam into the metal tube attached to IAC. it went away. idle was good once the seafoam made its way through. but after shutting it off and letting it cool. started up and the idle was back to what is was before the seafoam.

 

i dont belive you can bypass it. but in my situation i thuink it needs to be driven to let the seafoam in the feul tank do its job.

 

thanks to rpholz for your help. twice over. i would try seafoam and see if that help your problem. the wagon i have sat for a year or so. i think it is varnish build up in the system, that is what is causing my problem. hope this helps you.

Edited April 20, 2010 by dragonfire
spell check!!!

[84gl]

i've done every thing i can think of to my brat to fix this the only this i have not done is buy a new iav

[markjw]

If nothing else works,replace this sensor.It's a Coolant Temp. Sensor.

 

Located under the thermostat housing. A faulty one will cause bad idle and other problems.

 

Get a few at the wrecking yard 'cause they are kinda spendy new.

 

[GeneralDisorder]

Run a D-Check and see what you get for codes. Most of the sensors can be tested with a digital multi-meter and compared against specifications.

 

Do not remove the IAC. It is not an emissions device - it allows air into the engine so it can idle. Without it very little air gets by the closed throttle plate.

 

There really isn't much in the way of emissions on the SPFI systems. EGR and Evap. Purge solenoid's - that's pretty much it.

 

GD

Edited April 21, 2010 by GeneralDisorder

[ruparts]

Hi,

i agree with markjw on checking out the coolent temp sensor, and the connections to it sometimes get really corroded...this can cause a lot of issues with the FI . but i was thinking it was the one behind the intake runner on the right side of the intake manifold, with 2 wires. and thinking the one by the thermostat housing was for the instrument guage / indicator light. mine is mpfi not spfi so are they different on that?

also you might take the iav off and spray clean it inside, and put it back, they get stuck sometimes, its supposed to regulate a variable amount of air into the intake, depending on what the coolent temp sensor is telling the ecm your engine temp is.

[Crazyeights]

You mentioned "I blocked it off and it made no difference" I wonder if you might have an unmetered air leak between the MAF sensor and the throttle body. Is all the rubber intake ducting tight and leak free? Are there any hidden cracks or bad vacuum lines anywhere? Is the EGR valve partially blocked open by a piece of carbon? Just some additional thoughts to consider.

[smallwwb]

Thanks for the tips. The car sat for about a year, and has only been on two highway trips (total about 100 miles) since I got it running again.

 

I sprayed cleaner down the IAC body. Now it only varies when the car is warmed up. It does make a difference now when I pull off the IAC tube- seems to run better with it on. Checked for vacuum leaks, didn't find any major ones so far. Will check the sensors and EGR when I can.

Does the EGR and PCV system improve mileage?

Also, the car dies if I push the clutch in when the rpm's are up. If I give it a little gas right after pushing in the clutch it doesn't die. I think this might be linked to the IAC as well?

 

Will post updates as I get to it.

:banana:

Edited April 25, 2010 by smallwwb

[smallwwb]

Took the Subee on a 1000 mile road trip this week.

Still has the above problems.

[robm]

How about the throttle position switch? It is worth checking.

 

Clean the IAC really well. And maybe the MAF sensor, too, while it is all apart and you have your can of spritz cleaner in hand.

 

And look for air leaks, like others have said.

 

Would the O2 sensor affect the idle?

[smallwwb]

Checked Codes and I get Air Control Valve and Purge Solenoid Valve.

Do I have to replace these things, or can I bypass them?

I had the TPS adjusted and solved the problem with dying when pushing the clutch in.

Now it just needs to be given gas at startup and warmed up like an old carburetor.

Seems very low on power, but maybe that's because it only has 90hp:lol: