Hey everyone! First post. New to forum but not new to working on vehicles.
I have a 1989 Cherokee 4.0. Jeep has been great and dependable for years. Started ok but ran a little rough so I found Cruisers Renix page and started cleaning up the grounds just for good measure. Now, jeep starts better, runs smoother, and the lights work better than ever but I have a very low, hunting idle, 300rpm after it warms up and rythmically surges to 400 rpm. And because the idle is so low there is a hesitation off idle that causes stalling at take off.

I have been using cruisers renix tips and lunghd's sensor test page.

Things I have done:
1. Cruisers list: 1, 3, 4, 5, 7, 8, 10, 11, 14, 18, 21.
I did not do 2, 6, 9, 12, 13, 15, 16, 17, 19, 20, or 21 on.
2. New o2 (bosch) , new tps (adjusted correctly), new IAC, cleaned throttle body,
3. Tested MAP (.5 dc volts at source. .5 volts at wire A with key on engine off. And voltage drop to 2.7 with engine on) and hoses are clear an no cracks.
4. Tested MAT but got funny reading: .888 (that is point 888). Should beabout 800?
5. Tested EGR. Hoses are good. Tested the solenoid. Only opens a little when I rev it up. Ports are all clear.
6. New cap and rotor. Helped the running smooth out but not the idle. Old plugs looked good. No extra fuel or carbon build up. I also checked for arc-ing at night (none) pulled one plug wire at a time and all cylinders are firing. Good strong blue/white spark.
7. Cleaned and checked all CCV hoses. I found that vacuum leaks should cause a high idle, but I read in another thread about a guy that had replaced the rear CCV hose with a different elbow that was too small and rhe restriction was causing a low idle. That is not my case. My CCV is stock and clean. When I pull out the CCV hose from the cvalve cover it raises the idle to around 700-800rpm, but it still hunts.
8. I have not tested the fuel pressure. I dont have a guage yet. I do have a newer fuel filter.
9. I also tested all my relays:good.
10. I have not tested my coolant sensor, but I don't think that would cause a low, hunting idle.
11. I checked my vacuum canister for leaks by removing the hose off the intake manifold and capping off the manifold nipple. No effect on idle.
12. CPS. Jeep starts good so I didn't think it was the CPS bit I read in another post about how some guys have eliminated many problems with a new CPS. So, I got a new one at the local parts store and it made the jeep run worse! It barely started and shook like it was running on 3 cylinders. So I put the old one back in.

That's all I can think of right now. Sorry it's so rambling. All the stuff I have tried has started running together:-)

Thanks for any help you can offer.

 

Ref the #4 - MAT - what are you referring to here? EDIT..oh yes the manifold air temp sensor - test the MAT as mentioned in the link below..

http://www.lunghd.com/Tech_Articles/...iagnostics.htm

the MAT can also cause all sorts of problems.

Ref the #11 - the coolant sensor - the sensor might be bad in such a way that it always reads hot, causing the EGR to be on when it should not be.

have you checked for vacuum leaks using propane or a smoke machine?

 

I have been sort of in the same boat as you, but mine only acts up in the morning.
How does the engine act in the morning compared to the evenings?
Is your problem intermittent or every time you run your engine?
Funny about the new CPS making the engine run worse.
Let me know if you found any solutions?
John

 

Mr. Kelley it sounds like your on the right path. Doubt it's your problem but did u check the air filter? CCV systems are notorious for blow by causing air filters to be caked in oil. Steam or sea foam might help... Or loose/crappy belt?

 

Ok. Air filter is fine. Thanks for the ideas.

I noticed that when I start up the jeep, it idles normal, about 750rpm until it warms up. Then the idle goes down to the 300-400 rpm range. So, it looks like the low, hunting idle only happens when it is warm. Although, the stalling in gear happens whether the motor is cold or warm.

I tested the MAT and CTS using Lunghd's website and I got strange readings. I attached some pics of my meter. Maybe someone can take a look and make sure I'm doing it right.

The MAT tested at 3.0 ohms on a cold engine and .493 ohms when hot. The LungHd website says I need 185 ohms for a hot engine.
The CTS tested almost the same. .468 ohms on a hot engine.

Either both sensors are shot or I'm doing something wrong.

Any ideas?

 

following. and just curious, off topic, how are those 32's with a chepo lift?

 

Here's a reference:

 

Have you removed and cleaned the MAT?

I would see if that new Bosch O2 sensor is working and that it has heater voltage.

 

Thanks cruiser! That is the chart I was looking at when I tested the CTS and the MAT. My readings are not even close. I have not cleaned the MAT. I will do that now. Will cleaning the MAT help the sensor get a better signal? Does the sensor ground to the manifold? Could corrosion keep the sensor from grounding/making good contact with the manifold?

red4dr: It's a jeep so it won't ever handle great, but it has fairly new rubber bushings in the control arms, new tie rod ends and ball joints so it does pretty good on the road. The steering box is old. I adjusted it so it feels fairly tight. It still wallows/ follows the grooves in the road on the highway. Off road it does great.

 

Well, I cleaned the MAT. That thing was dirty. The idle seems a little better, not so low. I still get the same .465 ohms reading on a hot engine though.

I guess now the big problem is the stalling. I took it for a drive after it warmed up. It seemed down on power under load. I had a backfire/popping through the throttle body once under load but couldn't repeat it. Then, when I let off the gas to come to a stoop it would die. Starts right back up.

Thanks

 

One time I set a timer, went out to my Jeep, tested the CPS, plugged it back in, closed the hood and was back at the Puter' in 3 minutes. Why anyone with a Renix Jeep would not start by ruling out that trickster defeats me!

AC voltage CPS test; Small clips on the meter leads really helps. (you need contact with those little pins while it cranks)

Unplug the connector at the back of the manifold with wires going down to the bell-housing/cps. (it's a three wire plug, with only two wires)
Probe the two wires to the cps with the digital meter set on AC volts, a 200 scale on mine. Yours meter may have a lower 2 Volt, or “auto range”.
Crank the engine and note the voltage. (jump it if your battery is low) .35 is minimum. .4 to .8 is more like it.

 

Post 5 of my Tips?

 

DFlintstone: I forgot to add that I did test the CPS. AC Volts during cranking are .27. I know that is low for a CPS to work, but it starts fine. I thought, maybe mistakenly, that the CPS either worked, or didn't. That if a jeep starts, then the CPS is good. Mine starts and the CPS tests low. Can the CPS have an effect on idle/hesitation/stalling? The new, cheap, auto parts store brand made everything worse so I put the old one back in and jeep started right up.

If the CPS does have an impact on more than just starting, I can get a factory Jeep sensor from the dealer in a day or two for $75. I just don't want to drop the cash if the one I have works.

Cruiser: I tested the harness by probing the B wire at the TPS. No fluctuation in the ohms reading on my meter. I was thinking I might try cleaning the grounds at the dipstick tube again, but everything is clean and the crimps look good and I didn't get any funky readings... I don't know.

I will get a fuel pressure tester soon, just to rule that out.

Thanks for all the help.

 

That trickster can do about anything. Echos of condensers on point's ignitions!
I'd check it if my radio didn't work! You won't find that AC voltage test in any book, I learned it from Cruiser. I watched mine come down from .35 to less than .3 then, (and yes), started having a delayed start time. BUT, failing after warming up, or ransom stalls also happen.

Echlin# CSS980, from Napa is a pretty solid way to go there. Some were looking at the Standard PC307, supposedly advanced, or high altitude.. it IS cheaper, ($34 IIRC) but is not actually advanced. I carry one as a spare. I don't know what Mopar, (OEM) wants, but the Echlin has a pretty good record.

"canned";
To change your CPS I found if you BACK the fronts onto ramps, you won't have them in the way, where you need to lay. A stand under the left front frame would be in your way.
If CPS itself is putting out less than .35 Volts AC, unplugged, while it's cranking with a good battery, or the resistance is not 200 ohm's plus/minus 75, hot;

11mm socket > 3 inch extension > universal > long (18-24 inches of extension). Your feet are sticking out under the passenger side, you can reach up past the front drive-line with your left hand to hold the CPS from the front. Your right hand is on the ratchet way back by the tranny cross member. If you tie a long string on the old plug, you can use it to haul up the new. Toss that piece of plastic if it's still there, and do not drop the bolts in there! Echlin # CSS980, (from Napa, for 87-90), should be fine, but some prefer to go to Jeep. I wouldn't bother with anything else for that.

If your left forearm is bigger than a quart Mason jar, you might consider removing the front drive-line. Also You might cut your old CPS wires if they go through a deal on a bell housing bolt, then be sure your new are held somewhere safe.

The second one is REALLY easy!

 

Replace it with a good quality one and do the drill mod per post 7 in my Tips.