need help with surging idle

[3rd Q]

My '90 Q w/73k miles just started an aggravating thing. On a cold startup, the fast idle seems to stick- runs higher than normal and lasts longer than usual. Even after runining for a couple minutes, when I shift to drive it wants to take off like a race horse, or worse, the rpms jump up and down and sometimes wants to stall. Once it comes up to operating temps it idles beautifully and on subsequent warm start-ups there are no problems. I'm guessing it is something with the fast idle cam but don't know where to start.

I have done 8 new injectors, new plugs, fuel filter, all under plenum hoses/gaskets, knock sensors, plenum and TB cleaning this year so all those things should be good. I appreciate any help.

[DAEDALUS]

Check the MAF connection and look for vacuum leaks.

[Q451990]

I had an occasional problem with Q1 in cold weather start-ups where she would never "idle down" - but hold at 1500-2000RPM even after warm up. On most occasions I could turn the car off and then back on and it would fix itself. Then on one or two occasions I would have to disconnect the battery for a few minutes. In any case it was a control issue - not the fast idle cam.

Q45Tech once suggested that the ECU temp. sender or it's connection could be the issue. The ECU reads the engine temperature from a different sensor than the dash gauge - so if it's not getting the right signal from this sensor, the ECU could "think" that the car is still cold and hold the idle higher via the IAC valve. I don't think the problem ever showed up again after the Knock Sensor harness was replaced in 2001 - the ECU temp sensor shares this harness.

Heath

[3rd Q]

Thanks, guys. Heath, I did replace the harness when I did the knock sensors, but I'll check the connector again. Daedulus, I've been meaning to clean the MAF, so now seems like a good time to do it. I'll keep you posted.Paul

[3rd Q]

Hi all!

Just an update on this "surging idle" thing. I had begun to notice that on a cold start-up, the torque converter would seem to stay locked up when I hit the brakes, causing the rpms to surge up and down. My trans shop diagnosed it as a blocked trans cooler line in the radiator. I was planning on doing the external trans cooler anyway and since I installed it have had no problems with the idle.

Thank you all for the posts in years past on this subject. Seems like all the advice to be aware of the problem and to add the cooler was right on!Can't tell you how happy I am to have found NICO and you all!

Paul

PS. My trans shop recommended a Tru-Cool unit instead of the B&M. Said the design allowed for better cooling.

[Jesda]

Wow, I never would have suspected that. Good info!