So I got my 92 Cherokee about a month ago. It runs great when it's going but the problem is when you first turn it on. When it is first started it starts right up but unless you give it some gas nonstop for the first 5 min it will stall out. After it has had sufficient time to warm up like this I have no problems and even idling in traffic or at a light is fine. I replaced the battery when I first got it but since then I haven't done anything else to the engine. What the heck is causing this problem?

 

I'd check your IAC valve.. The pintle gets carbon built up on it (and the seat) and can cause poor idle. Easy to clean with some carb cleaner and a small stiff brush. Don't pull/twist on the pintle.

 

^ do that. It's a sensor on the throttle body. Extremely easy to do

 

Also you might try this just for fun:

The "Key Tricks"
Older (OBDI) models - Start with the ignition off. Within five seconds, switch the key on, off, on, off, on. ("On" is NOT "Start" and "Off" is NOT "Lock"). The "check engine" light will flash. Count the flashes. Each code is a two digit code, so a (for example) 23 would be FLASH FLASH (pause) FLASH FLASH FLASH (long pause). It will never flash more than 9 times, so watch for those pauses!
Codes are listed in "info threads" There's lots to check on a new Jeep, having the plugs gaped at .035 is one of them.

 

*Have you ever seen a check engine light? Even if the answer is no, I'd still see if you have any stored codes using the technique shown by DFlintstone above.

*I'd also be sure that all tuneup parts are fresh. Plugs, wires, cap, rotor, fuel filter.

*Be sure your charging system is operating properly. Low available voltage makes the engine management system do strange things to your idle. Watch the voltage gauge on your dash if you have one or use a multimeter. You should have approximately 13.5 to 14.0 volts with a healthy battery and a healthy charging system.

*Cleaning the idle air control and throttle body is really never a bad idea. Here's how.
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The Idle Air Control (IAC) is mounted on the back of the throttle body. (front for 87-90) 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

 

Thanks everyone. It was the IAC. I replaced and it runs so much better now. Now for some reason though my oil pressure is going up to 80 just running it up to 40 mph and 3500 rpm and it took a long time to drop. Any ideas?

 

Almost assuredly is the oil pressure sending unit. Located directly above the oil filter. I'd buy it from Jeep for the best reliability/accuracy/mating with your factory gauge.

 

Even though I didn't have this problem before I changed out the IAC?

 

Check to see that the connector for the oil pressure sending unit is not damaged and is in full contact with the sending unit.

The problem is there; start with a thorough inspection. If you don't find anything, you'll have to replace it.

 

Hi Everyone,

First time poster here. A few hours ago, after weeks of searching, I purchased a 1990 Jeep Cherokee Wagoneer Limited. 160,000km (Canadian). The body is in absolutely perfect showroom condition. Vehicle never has seen snow, but underside has typical surface rust.

Anyway - starting issue. Definitely has a little issue. As far as I know, this is fuel injected (as per manual) however, there's a throttle linkage under the hood much like it's carbureted. If I pump the pedal - I can get it to grab and it will run fine, but it's the initial starting...

The vehicle has sat unmoved for 9-months, so I'll have to replace seals, filters all that jazz... but I'm wondering if anyone can confirm if it's fuel injected (perhaps dirty injectors?) or other things.

I have a few other posts I'll be throwing up as well for those in the know.

Thanks in advance!

Proud New Owner,
Jeremy

 

Jeremy,

For a new issue, it's best to start a new thread.

It's less confusing for people trying to help the guy that started the thread and you will actually get more targeted responses yourself.

 

So something interesting happened. I did not get a chance to replace the oil pressure sending unit yet but after driving the Jeep for 5-10 minutes with the pressure at 75-80 it dropped to 40. At this point for the rest of my time driving it (about 2 hours) it stayed arond 35-40 and idled at about 35. Is this an acceptable oil pressure or should I still change the oil pressure sending unit?

 

Mine does the same thing.... not sure what it means though. runs fine dispite this....

 

I wouldn't lose sleep over it.

Get around to replacing the sending unit when you get the cash to. That doesn't seem like an accurate reading to me. You can always verify it with a mechanical gauge.