Idle Fluctuation

Tony71502 · 11-03-2009, 01:50 PM

When I start up the car at idle the rpm fluctuates almost to the point of stalling. This tends to go away after about 20-30 seconds. After that the idle fluctuation is about 50 rpm. There's no problem when the throttle is open even the smallest bit, not that I can tell.

Would this be as simple as a bad IAC? The IAC on there is only 2 years old and still clean.

Or could this be some tiny vacuum leak that almost fully closes as the engine warms up? 20-30 seconds doesnt seem like enough time to fully warm up from a cold start, though.

This ad is not displayed to registered or logged-in members.
Register your free account today and become a member on Mustang Forums!

mjr46 · 11-03-2009, 08:44 PM

make sure the throttle body is clean and the mass air meter is clean and no vaccum leaks

Tony71502 · 11-04-2009, 03:25 PM

Thanks Mike.

We cleaned out the MAF and IAC two days ago and that didn't help. I'll try cleaning the throttle body out. The TPS is fine. I sprayed a healthy dose of starting fluid around and there was no leaks. The only leak that I had was between the EGR spacer and the upper intake plenum. That's fixed.

The only codes in the computer are EGR and thermactor/thermastor related. No CEL is present. The codes are benign.

The car has power. Just the B cam in a stock block spins the 275's through second gear. Granted it was about 50 degrees out...

I'm going to grab a new IAC soon and see if that helps at all.

My intake system is 19 years old... I may just start upgrading.