Loping Idle,loss of power

I have a 89 cherokee 4.0 liter, Has run great since I got it, just recently I've noticed a considerable lack of power,decreased fuel mileage and it seems to lope at idle (kinda like a cammed out smallblock). It also seems to have a dead spot just off idle .When I hit the gas she dies a little then it goes. How do I pull codes out it? I dont even think it has a check engine lamp. I have access to a otc genysis obd 2 and 3 code reader. Maybe o2?

could be a few different causes:

vacuum leak
pcv clogged
ignition system malfunction
clogged injectors
head gasket leak
worn out timing chain
worn out camshaft lobes



start with these.

I forgot to mention this problem comes and goes on a regular basis

If it's intermittent, It's probably a vacuum leak. It could also be electrical, so check the obvious first, like plugs and wires, cap & rotor. Good luck

RNMCGUIRE said:

If it's intermittent, It's probably a vacuum leak.

Click to expand...

X2 sounds like vacuum to me. have you replaced the vac hoses yet. its time if you haven't with the age of your rig. if it were me i'd replace them all.

I made a set of plugs, a short piece of tubing with a screw in the end. You can plug off every vacuum line except the MAP for a test.
Loose manifold bolts. Be careful of the studs and even the bolts, they snap off.
Sticky IAC and a TB cleaning (keep cleaners and water away fromt the TPS).
The EGR valve will make it have a really low idle and even stall at low RPM's.
O2 sensor will mess with your idle as will the other sensors. There is a whole bunch of inputs for idle.
My largest idle improvement turned out to be, dirty connectors, for the O2 sensor, the knock sensor and the block temp. sensor. Next largest, was cleaning the grounds. I had a vacuum leak in my EGR transducer. Even a TPS adjustment helped some, along with a TB cleaning. And some new plug wires and an air filter.
Like I said, idle has a whole bunch of inputs, it often isn't just one thing.
Mine idles just a little low, but has a steady thump, thump, thump that I'm kind of proud of.

bcmaxx said:

I have a 89 cherokee 4.0 liter, Has run great since I got it, just recently I've noticed a considerable lack of power,decreased fuel mileage and it seems to lope at idle (kinda like a cammed out smallblock). It also seems to have a dead spot just off idle .When I hit the gas she dies a little then it goes. How do I pull codes out it? I dont even think it has a check engine lamp. I have access to a otc genysis obd 2 and 3 code reader. Maybe o2?

Click to expand...

Since nobody's suggested a plugged cat as the likely culprit, I'll throw that one into the mix. Bash the cat with your fist when it's cold. If it rattles like a can of marbles, you've found the problem.

Sounds like an EGR valve getting stuck, but thats just one of many possiblities.