Hey there, a forum newbie with a question here.
I've got a 1998 1500 4x4 with a 5.9L V8 with 160K miles. It's been running great since I bought it 6 months ago, but today it idled and accelerated quite roughly. Shortly after reaching normal operating temperature the problem suddenly went away, and the check engine light (which does illuminate briefly at starting like it's supposed to) did not come on while the engine was running. I let it cool for 3 hours when I got home and went out and took it for a short drive, and experienced the same rough idle and acceleration.

I haven't tried anything yet. I'm short on cash, so I'm trying to get prioritization advice--what should I try, and in what order? Any help would be much appreciated. Thanks!

 

When was the last time you checked / replaced the plugs, or did a good tune up?

 

I have not done anything beyond an oil change/coolant flush. I do not have previous service records for the vehicle (purchased 6 months ago).

 

Well, seems as you want to start cheap, id say pull the spark plugs and see how they look. if there nasty, replace em. Probably $30 for all 8 plugs.

Also, clean our your throttle body with some carb cleaner.

See how you fare after that.



Other things to check (More expencive):

Catalytic Converter: Listen for rattling sound while driving, hit with rubber mallet, again listen for rattle.

Plenum Gasket: pull off air box, open throttle plates wide open, using a flashlight look down into the intake, if you see a good amount of oil its blown.

 

Go to the parts store and get a TB gasket. Remove the TB and look around inside the manifold with a flashlight and mirror, so you can see all four corners. Opening the plates and looking down is a waste of time.

 

Thanks for the advice, guys. If the plenum gasket were blown, wouldn't my idle/acceleration stay rough no matter what? When I said the problem got better after reaching normal operating temp, I meant the rough idle/acceleration went away entirely for the rest of my drive home.

 

Sounds like tune-up time to me.

 

Not Necessarily, the plenum is a strange creature, depending on the severity of the gasket rupture(s), it can cause a variety of issues.

I would say just start with a good tune-up, plugs, wires, cap, rotor, pull the TB, get er cleaned up, air filter, etc.

If you do actually pull the TB to clean it, make sure you take Zmans advice and get a new gasket, they are $2-3 bucks, you don't want Leaks there.

 

Thanks again for all the replies. This might be a stupid question, but my service manual doesn't have any information on the plenum gasket. If I remove the TB and find that the plenum gasket is blown, how do I replace it? Do I access it by removing the intake manifold?

 

use the 1/4 plate haha i didnt nothing bad has happened yet. buttt everyone else will insist it for good reasons of course.. a good tune up always a 1+ clean the sensors in the tb itself my idle air control was way dirty with carbon i tried cleaning but ended up just replacing it . oh and theres an intire sticky thread to the plenum fix at the top of the list. also listen to theses guys my truck wouldnt be moving with out them there better then any mechanic ive taken it to except me of course