High Idle / No Start

[87 Jeep 4.0 Renix]

I have 2 issues going on and I don't know if they are related. First of all I have had a no start issue for quite a while now. I narrowed it down to the CPS and put a new one on a few months back. That resolved the issue, but this week it started again. I am getting no spark, but I can unplug the CPS and plug it back in and it corrects the problem. I checked the voltage at the TPS and everything looked within range. I put some dielectric goo on the connector to see if it helps, but won't know till I drive it a little more.

My second symptom that I don't know if it is related it that I am also having a high idle in relation to the start issue. It appears the throttle is open 3/16" when I look under the hood. You can't blip the throttle to get it to close, but I can manually push it closed with my hand. This makes me think this is mechanical in nature and not electrical.

Thoughts?

There was a TSB that addressed the CPS issue. It involved replacing the CPS and installing a patch harness going directly to the ECU, bypassing the C101 connector on the drivers side firewall. I can provide that for you if you like. But, I suggest unbolting the two halves of the C101 connector, picking all of the tar-like crap out of it, flushing both halves with contact cleaner, wiping it clean with a rag and putting it back together with dielectric grease applied.

Have you ever refreshed your engine compartment grounds? Many important sensors that give critical info to your ECU rely on these grounds. They must be clean, free of paint and grease, and shiny. Dipstick tube stud, back of head to firewall are the spots to refresh. Can't just look at them and a$$ume they're good. Remove, clean, scrape, polish. Then add dielectric grease to preserve your work.

Which connector is the C101?

A little bit of google searching and I found my answer. I would be interested in the mod if you have information.

Come on people.... Nothing?

Based on this thread, I would bet I have a vacuum leak. Mine is a mess.

http://www.naxja.org/forum/showthread.php?t=1033466

I have noticed that my idle is higher when the ambient temperature is lower. Does that make sense?

XJ throttle plate 101 (not to be confused with C101 bulkhead connector):

The throttle plate MUST be free to close against the stop screw.

The stop screw--3/32 allen--exists to keep the steel throttle plate from slamming fully closed and gouging the alloy throttle body. IT IS NOT AN IDLE ADJUSTMENT.

Ok, pull the intake tube so you have access to the throttle body and can view the throttle plate. DISCONNECT the throttle linkage and move the throttle to see if it is free in its full range of movement--if it is binding, or if the plate mounting screws are loose, repair.

Next, with the throttle plate closed as far as it will go against the stop screw, back out the stop screw until it no longer effects the throttle plate, then turn the stop screw back in while observing the throttle plate--when you see the first movement of the plate STOP. You have adjusted the stop screw correctly and are done with it.

Reattach the throttle linkage and reinstall the intake tube.

Now, adjust the TPS, its setting will have changed.

After you have done all of that post up your results.

Thanks Joe!

Obviously the throttle is not closing and more likely to do it in cool weather. I took the intake tube off and inspected the throttle body. It looked a mess was was very dirty with lots of gunk. The throttle plate was moving freely and I couldn't notice any obvious binding. I put some Seafoam in a spray bottle and misted the throttle body while running, but there was so much gunk I ended up turning it off and scrubbing the entire thing with a tooth brush. (Also poured some in the gas tank while I was at it) When I was done it was clean as a whistle. I didn't notice anything difference with the range of motion, but the Jeep was obviously running better. The stop screw appears to be properly adjusted. I reattached the TPS, adjusted it for .7 volts and called it a night.

This morning I started it again and it was running fine on start. The minute I touched the gas pedal the RPM's wouldn't come down. Obviously something is still sticking. I pulled over and checked the throttle linkage and pushed it closed. In neutral, the RPM's are screaming, but I could somewhat blip the throttle to make them fall some, but not near where it needed to be.

Thoughts: The spring on the linkage arm appeared to have significant tension, but could it not be enough to pull it closed? What else could causing this to stay open? Also, on your throttle body there are 3 cables, the throttle valve, the cruise control, and another mystery cable running into the firewall. What is it? What does it do? Mine don't appear to be moving, but rather bending at the connector on the TB .

Maybe related?

Sounds like you may have a cable with a busted strand, it will hang up in the "sheath".

Pull each of the cables off the throttle linkage, one at a time, until the throttle will fully close on its own, then pull the suspect cable out.

You might consider a motorcycle cable oiler, they work pretty well: http://www.amazon.com/CABLE-OILER/dp/B001PN41L0/ref=sr_1_fkmr1_2?ie=UTF8&qid=1286465016&sr=8-2-fkmr1

Also, from what you described, pull the IAC off the throttle body and clean the port.

Last, but never least, you have an EGR valve and they can go bad in a number of ways--stuck closed, you never notice; stuck open, runs like crap; blown out, intake leak and high idle.

Do you know what the cable does? Obviously it isn't working now.

Checked out my EGR.... It isn't connect to anything...

The cable through the firewall is to the accelerator--check your floor mats and the pedal assembly to see if something is hanging it up.

No vacuum from the EGR solenoid on the driver's fenderwell to the EGR?

The owner before me must have removed them because the vacuum lines have been removed and capped.

Not uncommon.

On we don't discuss defeating emissions equipment unless your vehicle is 100 percent off road.

However, it is the thought of numerous very sharp persons on this forum that the EGR on the 4.0--only used 87 to 90--was something like "Ts" on a boar hog, or equipment that really wasn't needed. When Jeep went to the 91 HO it was eliminated.

Me, I prefer to keep things working. With the current people running EPA there are vehicle inspections in ALL of our futures, I kid you not! Carbon tax, sound familiar?

I put a new cable on it and looks like it was the problem. That and I noticed the the firewall insulation was pinching the cable.

Glad you got it fixed.

Good luck.

TSB 18-51-88 is the service bulletin number. sorry but I haven't learned how to post up links.

I wouldn't rule out cleaning the C101 connector as suggested in the meantime. Lots of important signals run through that gunked up piece of crap to the ECU and other places, including, but not limited to:

TPS to trans
TPS voltage supply
Coolant temp
Air temp
Sensor grounds for MAP and others
O2 sensor heater relay
CPS ground
Injector grounds
O2 sensor
Knock sensor
IAC

Kind of important info that needs to be communicated between critical sensors and the ECU. I wonder why they eliminated it in 1989. Hmmmmmmmm.

cruiser54 said:

TSB 18-51-88 is the service bulletin number. sorry but I haven't learned how to post up links.

I wouldn't rule out cleaning the C101 connector as suggested in the meantime. Lots of important signals run through that gunked up piece of crap to the ECU and other places, including, but not limited to:

TPS to trans
TPS voltage supply
Coolant temp
Air temp
Sensor grounds for MAP and others
O2 sensor heater relay
CPS ground
Injector grounds
O2 sensor
Knock sensor
IAC

Kind of important info that needs to be communicated between critical sensors and the ECU. I wonder why they eliminated it in 1989. Hmmmmmmmm.

Click to expand...

Definitely agree with Cruiser54 on this. And you might as well get after cleaning the backside of the fuse block while doing this--they will both need it.

Other than tracing the wires, cutting, and splicing, is there any good writeups on removing this connector?

No need to remove the whole connector. Just clean it as was suggested. It's normal maintenance as far as I'm concerned. Maybe only once in the Jeep's life......... I have bypassed the C101 with my CPS wires. Not a bad job. I could walk you through that. Got a multi-meter?