Chevy TBI idle problem (1 Viewer)

[dallen341]

I just fired up the new Chevy 350 TBI in the FJ60. It is a 1991 motor using the painless harness. It runs fine but I can't get the idle to drop. I followed the idle adjustment procedure (Jump "A" and "B" on ASDL, turn key on, wait 30 seconds, diconnect the IAC harness, fire motor and adjust throttle plate for minimum idle).

That all works fine, but as soon as I connect the IAC harness and pull the "A" - "B" jumper on the ASDL the idle creeps back up to 1000 rpm's. I can drop the 700R4 into "R" and the idle does drop to 825 or so but creeps back up to 1000 rpm's with 20-30 seconds.

Coolant temp registers 195-200 degrees so I suppose I can rule that sensor out.

Timing is set to zero with the spark control wire disconnected (tan wire).

Anyone have a clue what to do next?

Thanks...Don

 

[Dynosoar]

I think you need to pull the jumper out before you reattach the IAC.

Dynosoar

 

[inkpot]

Howdy! Have you tried doing the "reset" on the IAC? You can resposition the plunger , but I don't remember the exact process. My son used to have a 91 Camero with this setup. He sold it before we got it totally debugged. At times, it would just idle high like yours, at other times the idle speed would float between 550 - 1200 about every 6 - 8 seconds. After replacing/adjusting everything we could think of, he sold it without fixing it. I think it was possibly a vacuum leak around the rear of the intake manifold. That's the only place we could not reach to test. Good luck. John

 

[dallen341]

I did pull the jumper before connecting the IAC. I can see the IAC registering on the scanner.

Thanks

 

[Elbert]

I belive the ECM controls the idle via the IAC motor.... I did not think the idle could be adjusted?

I think the reset just gives a baseline.... The ECM still controls the idle?

Whats the idle RPM now and what it is doing?

 

[brokenparts]

This might be a stupid question but did you let it warm up fully?

 

[Elbert]

I have a 92 K1500 350 TBI.... cold it will idle around 1,000 rpm, warm it idles around 600-700 RPM. With th A/C on it will increase the idle just a little. I had issues with the crappy plastic vaccum lines on the EGR solonoid one time...you might want to just replace those with old schoo vaccum hose. THose plastic lines just break and sometimes they are hard to notice. Generally I would check for vaccum leaks. What is the idle at full operationg temp?

 

[dallen341]

Update.

The idle issue when warm was idle at 1000 rpm's and would not drop. When I dropped it in gear, the idle would drop to 825 or so but creep back up to 1000 rpm's.

There is an idle adjustment, however it is a minimum idle. The IAC is forced closed by jumpering "A" and "B" on the ALDL, turning the key on for 30 seconds, disconnecting the IAC connector which prevents teh IAC from moving, and then setting the idle. All that worked fine, but when returned to normal running condition the idle would go back to 1000 rpm's.

At this point I suspect it is my scan tool that is causing the high idle. Every time it idled high the scan tool was connected. Last thing I did yesterday before I ran out of time was let it run without the scan tool connected. I seemed to drop down to a normal idle range. I have a tach somewhere that I need to find and connect and see where I sit.

That's if for now...Don

 

[dallen341]

Update #2,

Tom at Turbo City located in the City of Orange California has confirmed for me that when the scan tool is connected and is in diagnostic mode (allows reading of current information), the scan tool commands the engine to idle at 1000 rpm's. The 1000 rpm's is part of the diagnostics.

Imagine that...it works properly!

thanks all...Don