'99 Stalls at idle

Hi all
I've been working on 99 with a 3.4L, auto trans,that stalls regularily at idle when at operating temp. The MIL is on with cde P0172 rich. Long term fuel trim is at -40 at idle but levels out at -5 at highway cruising. I've cleaned the maf, which is reading within specs, O2 are fluctuating bet 0.05 and .9 volts. No vacum leaks that I can find, fuel pressure is at spec with koeo but I can't check it with engine running.
Any ideas?

Leaking injector
Engine coolant temperature sensor <- First thing to check
Check spark in all cylinders

Mine (92 3.0L) was doing the same thing and I had the injectors cleaned and they found two vacuum leaks as well and it fixed the problem.

Hi all
I've been working on 99 with a 3.4L, auto trans,that stalls regularily at idle when at operating temp. The MIL is on with cde P0172 rich. Long term fuel trim is at -40 at idle but levels out at -5 at highway cruising. I've cleaned the maf, which is reading within specs, O2 are fluctuating bet 0.05 and .9 volts. No vacum leaks that I can find, fuel pressure is at spec with koeo but I can't check it with engine running.
Any ideas?


Read where you stated that you had cleaned the AFM but what about the inside of throttle body where gunk builds up around throttle valve plate on inside......when it builds up there it will not allow enough air to pass by throttle plate which causes richened fuel mixture at idle which is always more noticable when engine is warmed up :o)