M50 Idle surge on start up for 20-30 seconds

[richardb]

Hey guys-
Need some help. I had idle hunting problem with my car recently, I swapped out the MAF sensor with a spare just to cancel that out.

I had some cracks in the rubber intake elbow, and just replaced that with a samco silicone intake boot from Turner.

I have also cleaned the idle control valve with cleaner.

When I first start the car (hot OR cold) it idles high about 2500 rpms for 20-30 seconds then the idle settles back down and is completely normal.

I sprayed around the booster/intake/hoses with carb clean to see if it sucked in the fluid and would idle up. It did not.

Any idea what to replace?

[mega_t2008]

Try to measure resistance on your Engine Coolant Temp sensor...

[richardb]

Ok... I have the brown m20 coolant temp sensor in the cylinder head. Could this be causing problems? I bought it from the dealer new last October when I finished the swap.

[mega_t2008]

It depends... Normally, we use that on m50 swaps for temp gauge on your IC... But you have to know that there are two sensors in head of your engine... If you are looking to your engine from the drivers seat, then M20 ECT sensor should be the one that is first of you, and front closest to timing chain is for DME... So where have you installed yours???

[e30s50dan]

I don't think you get them backwards. One has bigger threads. Maybe you have them plugged in backwards

[416stroker]

Ok... I have the brown m20 coolant temp sensor in the cylinder head. Could this be causing problems? I bought it from the dealer new last October when I finished the swap.

No thats just for your cluster to function

[mega_t2008]

To clarify, try to check if you have interchanged your ECT and Temp Gauge connectors...

[richardb]

I will check it when I get to my parents this weekend. The gauge in the cluster functions fine...

[Adrian_Visser]

I don't think this has to do with your coolant temperature sensor. I wouldn't look past vacuum leaks or a bad ICV just yet.

Maybe try a spare ICV if you can get your hands on one.

Another very thorough look for vacuum leaks is a good idea too. Check around your injector o-rings and try disconnecting your booster and plugging the hole into the intake manifold and see if the problem is still present.

[richardb]

I'll update this as hopefully it will help someone out. The problem ended up being the throttle position sensor. Installed a new one in July, and voila problem gone.