Soybean

Hey guys I have an 87 Jeep Cherokee 4.0 with an automatic trans. When I start it up the idle is a little high but then settles down, (I heard this is common), but after I drive it and put it in park or neutral it idles a lot higher than normal. It is also very sluggish under acceleration and seems to be held back. What could cause these? It also runs very hot, to the point where when I open the hood and try to get the hood latch open it almost burns my hand. I'm scared it's going to blow up soon or something.

DFlintstone

You might start with the Idle air control, (below). Also I see you have an 87. You might want to go ahead someday and deal with your c 101 connector. If you click in my sig, there is a thing on that there.

Cruiser is this your IAC writing?, If so, should I put it with the others?

IAC CLEANING 88


The Idle Air Control (IAC) is mounted on the back of the throttle body. The valve controls the idle speed of the engine by controlling the amount of air flowing through the air control passage. It consists of a stepper motor that moves a pintle shaped plunger in and out of the air control passage. When the valve plunger is moved in, the air control passage flows more air which raises the idle speed. When the valve plunger is moved out, the air control passage flows less air which lowers the idle speed. Over time and miles, the IAC can get carboned up which can have an adverse affect on idle quality. Cleaning the IAC may restore proper function and is an easy procedure to perform and good preventive maintenance so it is never a bad idea.

CLEANING THE JEEP 4.0 IDLE AIR CONTROL

Remove the air filter cover, associated hoses and the rubber boot that goes from the air filter cover to the throttle body. Remove the IAC with a torx driver (2 bolts; one can be kind of hard to get to)

“Gently” wiggle out the IAC from the throttle body. Gasket on the IAC can be re-used if it is not damaged

Clean the IAC with a spray can of throttle body cleaner; inexpensive and available at any place that sells auto parts. Throttle body cleaner is recommended rather than carburetor cleaner as it is less harsh, safe for throttle body coatings and is best for this task. Use cleaner, a rag and a toothbrush and or Q-Tips. Be gentle; don’t twist or pull on the pintle that protrudes from the IAC as it is fragile and you could damage it.

Thoroughly spray clean and flush where the IAC seats in the throttle body with the same spray cleaner

It is also a good idea to clean the entire throttle body itself, the butterfly valve inside of the throttle body and all associated linkage as long as you have things disassembled

Reinstall IAC and check idle quality.

Soybean, is your E-fan coming on? It comes on at like 217*, and when the AC or defrost is on...Also you should have a fan shroud....

Soybean

I have already removed and cleaned the IAC and checked the connections.

Soybean

I have not checked the voltage though. Should I do that? Would it cause it to run hot and idle high after driving?

DFlintstone

I (in the most dastardly fashion), copied and pasted! A PM from Soybean.
Yea I'm bad. .

"Haha yeah I apologize for not paying attention to the vacuum line to the MAP. "

DFlintstone

Besides getting that E-fan working, I wonder if your mechanic has a point. Anybody else here of the EGR valve sticking open after it's been hot?

Radi

yes. For that matter they don't operate at all when the engine is cold...or at least aren't supposed to. Most have ECU based temp. control or a simple thermal vacuum switch. Not sure which one Jeep uses.
But I have had the solenoids on the electrical ones bind right up when they overheat. Don't recall a similar problem with the vacuum operated valves. Just not wanting to seat..

DFlintstone

Yea, our Renix is vacuum. (I think my line fell off and somehow seems plugged up, years ago).

So if it didn't seat, that vac leak, (to the exhaust) could account for high idle. But, since we can trust soybean, word for word to tell us accurately what is, or isn't happening he posts, "When I start it up the idle is a little high but then settles down".

So, after it cools it might seat?

Separate side note. MY idle, (On my 90) has recently been high now and then..putting off the IAC cleaning...just ..I saw another post or two, I wonder if the "summer fuel" cruiser mentioned might be involved...

Soybean

Lol man you guys are rippin me. I'm just going to replace the EGR since its about 25 years old anyways. When I start it up and its cold the idle jumps like always but settles down within 5 seconds. After driving even 5-10 minutes when the Jeep is in park or neutral its idles probably around 2000-2500 RPM I'm guessing. When I jam the brake to the floor the idle dies down, and when I run the heat full blast the jeep seems to drive better and not be so bogged down.

DFlintstone

.....sounds like a good...Idea.....I might look at it and see what it looks like myself, then take a pic so it so cruiser can see it.....

Vacuum leaks suck. I go around with short little shots of starting fluid, if you hit one the sound of the engine will change. Small little shots! You don't want that stuff to accumulate. It's a fire hazard, but It evaporates right away. Also with a tube, or a section of hose you can listen for it. Don't forget the lower O rings on the injectors need to seal as well. (uppers would leak fuel).
The manifold bolts have a habit of loosening, especially that rear one. On anything like that you never want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I go over about three times. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep.

2500 rpm?...man...I don't have the experience to say you should replace the IAC. Rule out vac leaks. probably a good a idea to follow the TPS instructions in my Sig, (which include cleaning the TB). Guess you already went through your c-101 and the grounds?

Radi

You know...it's odd the stuff that happens. I've had a couple of vehicles suck up a golf tee of all things in that vacuum line. It's the strangest thing. I don't even golf.

cruiser54

Do this. I'm betting your TPS is bad, the ground circuit is bad, or the tPS needs adjustment. Read the following instructions carefully and do what they say. Don't wait for another 10 posts when Flintstone suggests teh same thing I am now. LOL.


Have you ever cleaned the C101 and done a ground refreshing? If not, I wouldn't spend another dime on parts til it was done.


RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS be sure the throttle body has been recently cleaned. It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
IMPORTANT NOTE: With the Key OFF, and using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS. The letters are embossed on the connector itself. Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it parallels the valve cover and also over near the MAP sensor on the firewall. If you see more than 1 ohm of resistance, or fluctuation in your ohms reading, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding. I can provide an instruction sheet for that if needed.
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body. This manual transmission vehicle TPS provides data input to the ECU. The manual transmission TPS has three wires in the connector and they're clearly embossed with the letters A, B, and C. Wire "A" is positive. Wire "B" is ground. Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors. Note the voltage reading--this is your REFERENCE voltage. Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For example: 4.82 volts X .17=.82 volts. Adjust the TPS until you
have achieved this percentage. If you can't achieve the correct output voltage replace the TPS and start over.
AUTOMATIC TRANSMISSION: RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-wire connector, same as the manual transmission vehicles have, and it is tested the same as the manual transmission equipped vehicles—FOR ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector clearly embossed with the letters A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module. Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your REFERENCE voltage. Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage. For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage. If you can't, replace the TPS and start over. So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and the other side feeds the TCU.
FOR AUTOMATIC TRANSMISSION RELATED ISSUES. Check the four-wire connector side of the TPS.
If you have ENGINE issues check the three-wire connector side of the TPS. For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.
Revised 05-28-2012

cruiser54

It was ME who suggested that first!!!

And Don, the IAC cleaning write-up is not mine.

DFlintstone

Ha! Yea, I had in instructor...now and then he would loose a small ball bearing in there. I real bummer when its plugged, and looking at it you can't see a thing!

HA! Gotcha! (read the bottom of post 10 again.) (you taught me well enough to shoot back!)


I often spend 5-10 minutes typing a post, a bunch of these little symbols, (letters and numbers, all look the same to me!). Amyway, good call!

Soybean

Thanks guys, I will pick up a ohm meter today hopefully and do what cruiser said.