Engine Performance problem
2002 Mercury Mountaineer V8 All Wheel Drive Automatic 107000 miles
The engine has a habit of running rough during warm up. It does not do it with every cold start up but is getting close. It does not miss consistently. It will run smooth for several seconds and then miss once. It will run fine for 5 seconds miss once or twice. It can miss randomly for 5mins but never in a consistant pattern. It misses at all rpms (except idle) and at load and no load on the engine. The problem tends to go away once the engine is at operating temperature but not always.
Here is a list of things I have tried.
Cleaned the MAF sensor.
Checked air filter
No codes on the OBDII tester
O2 sensors good
Checked all the resistance on the coil packs
Checked all the resistance on the fuel injectors
Cleaned the ERG valve
checked for vacuum leaks
Checked the fuel pressure regulator
Checked the fuel filter
Checked the fuel pump
Checked the fuel pressure in the fuel rails
Checked the idle by pass valve
checked the PVC valve
Checked the thermostat
The tps is 20K miles old.
The fuel filter is 25K miles old.
The fuel injectors were professionally cleaned 25K ago.
No check engine light.
I have spent many hours troubleshooting this and the problem has been going on for about 30 days off and on-slowly getting worse.
I have learned that I have a limited amount of time to diagnose the problem before it goes away for some reason. It typicaly "fixes" itself after an engine stop/start cycle. Once the problem goes away, I have to wait until a cold start to create the problem again. Once the problem goes away the engine runs perfect as long as it stays running and never goes back to missing until it cools down.
Any advice would be helpful before I take it into a dealer and spend hundreds of $ trying to fix it.
have the same problem?
Saturday, June 13th, 2009 AT 11:26 PM