92 2.4L MM running bad

[Merritt]

Hopefully some of you can help me get this figured out. My truck is skipping and I've just done a tune up trying to get it to stop but no luck. It's skipping at part throttle, and most of the time it goes away when you give it a lot of gas. Once in a while the truck will run smooth, but it seems to only be when it's cold and not up to operating temperature.

The tune up consisted of the following:

New plugs gapped at 44 thousandths
New plug wires
New cap and rotor
New fuel filter
New coolant temp sensor
New thermostat
Cleaned the egr valve
New PCV valve
New air filter

Anybody got an idea what to look at next, anything important I missed during the tune up? I really appreciate any help I want to get this thing running right so I can focus on lowering and paint. Thanks!

James

[pennyman1]

I would clean the throttle body real good and make sure all bolts and nuts are tight on intake and exhaust. Run some Redline synthetic fuel injection cleaner through it - the whole bottle in a full tank of gas. Depending on the mileage, change out the O2 sensor. Also make sure all vacuum lines are good and attached where they belong.

[Merritt]

I will check all the nuts, bolts and vacuum lines. I'm gonna clean the TB tomorrow, I was going to when I did the tuneup but I ran out of time and energy lol. If the oxygen sensor's bad can I unplug it and see if it runs better, or will it run like crap anyways?

*Edit: Truck has just under 83k on it, but with it being 18 years old I can see the oxygen sensor going bad.

[camoit]

Also check the charcole canister for cracks. AKA Vaper recovery canster. Oh and there is some vacume lines at the fuel tank.

[Merritt]

Thanks camoit will do. I got in the truck last night and left for work, as soon as I started it up it ran good with no skip. By the time I had gotten to the first stop sign, (about 1/2 mile or so) and took off from there it started skipping again.

[camoit]

That tell us that it must be warm befor it starts missing. Now what circutes in the vacume system only come alive when it gets warm?
Didn't you say that it only happens at a cruse?
At whar RPM range does it happen at?

[Merritt]

No not just a cruise, it does it through all the gears. It's not as noticable in first since it's such a short gear, but second it will bog down in the low rpms, but it seems like once I get through the low rpms and once I give it some more throttle it clears up. It'll do it cruising too, but just give it some more throttle and it clears up. It doesn't have to warm up all the way to operating temp for it to start skipping, it seems like I can just drive for a minute or two and it starts.

I'm still getting to know the truck, I've only owned it a couple weeks, or I'd try to give you more info. I'm going to clean the tb in a little, and check all the vac lines. I unplugged the oxygen sensor and drove around with no change at all so I don't think it's that. I'll keep you posted when i find more out.

[Merritt]

OK I cleaned the TB, checked all the vacuum lines, ran some seafoam in the brake booster, and cleaned the MAF. All the vac lines looked good and they weren't brittle, but after all of this it's still skipping. It's running a little stronger, but the skip's still there. I took it up the road and going up a hill in fourth it started to skip, so I gave it more gas and it cleared out. My rpms didn't move, so with it clearing up after getting more gas, it leads me to believe it might be a fuel delivery problem.

Next fillup I'm going to run some seafoam in the gas tank, I'm keeping my fingers crossed that it's just a little gunk somewhere in the fuel system somewhere, and the seafoam will clean it up, even though that's not very likely. How can I check the injectors individually?

[Merritt]

Seafoam seems to be doing the trick, must've been an injector clogged up. It's still skipping a little, but I can barely notice it now. I'm gonna go by the parts store and get 2 or 3 more cans of it and run it for the next few fillups, maybe it'll clear itself out and I won't have to spend any more money on parts.

[LSR Mike]

Change your Fuel Filter.