My 4.2 L engine has begun to run rough after stopping while in drive after about 20 seconds. I have replaced the two front oxygen sensors and have also checked the wires and plugs, any ideas

Dave

 

Hi buildtek and welcome to FTE

Does it miss or the idle slows way down or? If you just start it up and let it idle what does it do? Is it worse hot or cold?
Does the check engine light ever come on?
Any other symptoms?

 

Hi Dave,

Thanks for the welcome

The engine misses after it warms up, almost to stall point, and only under load while transmission is in drive with vehicle stopped. Engine runs fine at idle/neutral and acceleration. The “check engine” was activated with a too lean condition; I then replaced the two front O² sensors. Seems to run better but problem persist. No other symptoms.


DKH

 

You might have more than one problem.
It sounds to me like you might have an IAC problem. You can try removing it and cleaning it to see if that makes a difference. It is bolted to the top of the intake manifold with 2 bolts. You can clean it with some Carb Medic carb cleaner.
While you're cleaning things you should clean the MAF sensor as well and check for air leaks between the MAF and the throttle body. To get at the MAF you remove the air cleaner housing like if you were changing the filter. Take a look in the hose that goes to the throttle body on the engine. You will see a rectangular shaped piece with 2 thin wires that look like light bulb filaments. Clean these with some Carb medic as well. Usually spraying them will clean them off. You want to get rid of any "fuzzies" on them but you dont want to actually touch them with anything much as they break quite easily.
You might also want to check for a vacuum leak. Check all your vacuum hoses and see if they are all attached and not cracked or anything. You can take some Carb Medic and with the engine iding spray it at the intake manifold where it bolts to the heads, where the throttle body bolts to the intake, at any vacuum hoses etc. If the idle changes at all, either up or down, you've found a leak.
Let us know what you find.

 

Thanks for the information! I'll check it tomorrow while I’m at the local motocross race track. I will let you know what I find.


DKH

 

I cleaned the sensors and the IAC, I then did a vacuum leak test with contact cleaner and I found a small house on the intake manifold directly opposite of the IAC, which had a 3/16 hole in it. Since I didn’t have a replacement hose with me I patched it with a radial tire patch. Engine runs smooth now. Thanks very much for your help. I owe you one. If you ever need any CAD work done, let me know.

DKH

 

CAD work eh? hmmmmm
lol
One of these days I want to draw out the front suspension of my race car to figure out the roll center, camber curves etc.
If there wasn't good instructions in books for doing that I might take you up on your offer

Good to hear that you got your truck running better again
Thanks for letting us know what you found.