Thanks guys, that is good information. I will grab a new CPS at napa on the way home.

I hope that takes care of my issues, but Doh! I will feel like such a moron if it does. Everything I have read on this and other forums said to check the CPS first...

I will post results.

 

Drill out the upper mounting hole!!

 

Update: I got a new CPS, Echlin brand at Napa, $37. Installed it and nothing happened. Jeep didn't start. Tested voltage:none. Drilled out the top mounting hole and it started right up putting out .47 volts.

It helped the idle a little, it still idles low, hesitates, stumbles, low on power.

I also checked the fuel pressure. I get 40psi with key on ignition off, and 30 psi running. Pressure goes up with rpm. I didn't check the leakdown. So far it looks like i have good fuel pressure.

Ive been reading everything i can find on these issues and it seems like every other guys solution isn't mine. Frustrating.

Also, I've been under the hood so much I've noticed a knock that i nev see r heard while driving around. I don't hear the knock when i start the engine and it's cold. As soon as the motor warms up the knock starts up and gets louder as it gets warmer. Can't hear the knock in the cabin when driving. Could a bad enough knock tell the computer to retard timing? Could it be something mechanical like a sticky lifter or rocker?

Thanks for all the help!

 

I had the same issue on my 88-no power, backfiring, low idle, almost stalling. I checked my grounds and cleaned C101 -it was a real mess and I'll definitely be doing the hard wiring trick soon. It has been fine so far since. I'm curious to see what you find with your Jeep.

 

At least the CPS is ruled out, (and more trouble around the corner avoided). So the unplugged CPS put's out 4.7 acv when you crank it.

Fuel pressure sounds good. 39# running with the vacuum line on the regulator, about 10 less with the line off is what you want to see.

"When I pull out the CCV hose from the cvalve cover it raises the idle to around 700-800rpm, but it still hunts."

So the idle comes up with enough air. Gotta be suspicious what your Idle Air Control is doing.....

Interesting thought about the knock and the sensor, but it's my bet it's designed to maintain idle even at it's most retarded timing.

Notes: Mine seems to run fine if the MAT is unplugged. Likewise with the 02 stone dead, (same as unplugged), the only noticeable symptom was a 20 second "seeking" cycle for idle. (and bad mileage)

See what Cruiser says, but that IAC, and it's wires and/or plug might well be your issue.

I've never checked my MAT, other then it's ground, not much help there, at least at this point.

 

Update: I also checked the ECU inside and out. It was perfect, looked brand new. It didn't help anything but now I know for sure it is not the problem.

Ok, here's a question for everyone: I replaced my IAC with a new one, (I can't remember what brand, got it online before I learned about buying quality sensors) but there was no change in idle or rpm. So, I put the old one back on, assuming it was good.

DFlintstone: should there be a change in idle if I unplug the IAC while the jeep is running? When I unplug mine there is no change in idle quality or rpm. I thought there would be since the computer controls the idle with the IAC. The throttle body is clean and a vacuum leak increases the idle speed, so if the IAC was working correctly shouldn't the idle decrease, or the engine die, if the IAC gets unplugged and the pintle isn't being controlled by the computer?

Also, I didn't have this low idle/ loss of power/ hesitation until I started Cruiser's list. I'm wondering if I messed something up when I was pulling plugs, cleaning grounds, adjusting wire harnesses. Maybe I'll go back and check my work...

 

If you unplugged the iac it should keep running at a relatively consistent rpm. Here's a test for you- let it sit untill at start it is idling around 750, unplug the iac and go for a drive. If the idle continues to drop, then your issue lies elsewhere. Out of curiosity, how's the map sensor? If your getting backfires the map could be not reading properly and dumping fuel or running very lean. It would stand to reason because if you have a stall when you stop or try to give it gas and hesitate then possibly fuel could be your issue and not air.

 

No....it's motor works that "pintel" in, or out to control airflow. Unplugging it just leaves it where it is. When I had isues with mine, (high idle), removing and cleaning it didn't help for long. Later I figured out I had a bad connection at the plug.....so bad that just pulling it off and putting it back didn't get it. Since the socket on the IAC faces up, I was suspicious at some point it got water, or coolant in there.

Maybe later I'll have some time to poke around, (remove mine and watch it move), check my own MAP values...

You do have around an ohm or less from the sensor ground circuit to bat. Neg. You are confident you have the TPS set correctly on the flat, engine side connector. Plugs are gaped to .035.

Generally it runs fine, just it has issues at low RPM/idle?

 

Been doing a little homework on that IAC. All four wires go straight to the ECU. I though I'd pull mine out and (carefully) test it with a 6v feed, or maybe a 9V battery, but found this.

I don't want to risk extending mine more than 1/4 inch, so I canned that idea!

 

Then I found this on the latch relay. What it says is that power is provided while cranking, then for a few seconds after shut down. It doesn't make clear that the relay is necessary for function, but if I had idle problems, (especially low idle) with multiple IAC motors, I'd make darn sure that (third from the front) Power Latch relay had a clean socket to plug into. CRC electrical contact cleaner, spray, insert a relay, jiggle, remove, spray, repeat. (they, all four swap, I usually suggest swapping in the AC relay)

Sorry "screen shot", took me a long time to find it, then lost it!

 

I might sneak up to the back door and ask a teck if he has a Miller #7558 tester. (bring a 12 pack!) Mostly kidding, but here is the procedure;

 

I'm sure plug gap can cause crappy idle, maybe Cruiser or someone can chime in on if that is possible with a tps issue.

 

(from post #5)...You are set on the 2 ohm scale? Select a scale that is higher than what you are testing, like 2000. Yes I see the "K", but I also see the decimal point.... Maybe check the manual.

 

DFlintstone: That information is incredible! Thank you for taking the time to research that. I have not even touched the jeep for a couple days because I have been so frustrated. All that great info looks like it came from the Factory Service Manual? Correct? Looks like I need to invest in the FSM. And maybe a "Brick", that is what my buddy calls the Snap-On MT2500 scanner. I just don't have $3000. Although, I am so curious to know what is going on with this jeep I am actually considering dropping the cash. If I could find one.

I bought a new IAC and replaced the old one and there was no change in idle/stalling. So, I put the old one back on. Plus, all this low idle/stalling started after I cleaned grounds and plugs. This makes me think my problems might be connection/harness/ground related, instead of a bad sensor.

My meter is strange, I don't have the manual and I am not real good at using it so I don't know how to change the range. I will try to get some more info about it. That was one of the sensors I tried to test but wasn't sure about.

I was able to swap the MAT sensor with another used one from a friend. I got the same reading on my meter and there was no change in idle/stalling.

Thanks for all the help.

 

Instructions for meter:

https://learn.adafruit.com/multimeters/