'88 XJ, 4.0L Cold-start/run problems

Hi! I haven't posted for awhile . . . . it seems that, over the past week or so, my '88 XJ (4.0L, AT) is having cold-start/run problems. When I first start it up (in the morning or after several hours of its being off), it basically cranks as usual but won't keep running unless I keep my foot on the throttle. It runs quite rough, like a miss, and, if I let it die, it takes quite a bit of cranking to re-start it. After it thoroughly warms-up to running temperature it seems to operate normally except for a very subtle roughness . . . no more holding the throttle or dying, etc.

I've been too busy lately to deal with this or to even really think it through . . . . . 'Seems like some sort of heat sensor . . . I've also pondered things like dirty throttle body, O2 sensor, and, for reasons I can't explain, the never-before-replaced-or-given-trouble fuel line pressure regulator keeps slipping into my thoughts . . . . .

I'll probably get to doing some checking this weekend . . . your suggestions are appreciated, as always!

TIA! Don

It fun being an owner of a 88 XJ, I know all about it.

I had a similar problem. I'd recommend you have the throttle body cleaned to make sure the idle air controller passage is clean.

Over the weekend I changed my Idle air controller. I figured after 16 years it was due for repalcement. My XJ does idle much better, especially when you crest a hill and coast down the back side.

I'd also consider replacing the the Manifold Abs Pressure (MAP) sensor. This tells the computer how much air in flowing through the intake by measuring the vacuum. You may want to make sure the hole for the map sensor hose in the throttle body is clean of crud when you have it cleaned.

Once you do those and you want to continue th sensor renewal program then I'd repalce the inlet air temp sensor, it in the manifold. Mine was slimed with oil from the Crankcase vent system.

Each of these sensor changes may make a small change on you will notice. I woudl consider the new Idle air controller, might even consider changing it before you have the throttle body cleaned. While you have the old IAC out you can inspect and see how slimed the seat the pentle has to set on is. Mine was not bad so I passed on cleaning the throttle body over the weekend and installed the new IAC.

I paid $60 for the IAC, figure $30-$60 for a MAP sensor, and $20-$30 for an intake air temp sensor.

As always, Martin, thanks so much for the good suggestions! I'll work on some of those this weekend. Others, I'm not so confident with, I may take to my mechanic. BTW, I neglected to mention that, lately, my mileage has been cr*p . . . 'likely it all fits together. Yes, you're right, the '88 has it's challenges . . . but, I love it . . . it's actually been pretty good to me in the 302,000 of its 352,000 miles I've owned it.

Okay I give up... Martin you've convinced me that it may be time to clean my intake manifold as well. I'm in Seattle right now and my FSM is back at home in JAX. Does it provide the steps to do it? I've still got that really annoying low idle (like 500-600 rpms) and that might be part of the problem.

You have a fuel delivery problem. Get a Chiltons and follow the sequence for testing the the fuel system. Also do the the test for the EGR system. Post back with results.

Hawaii,

I have had the dealer tech do my throttle body cleaning. He would remove the throttle body from the intake then used a brass brush to get the slime off the back side of the throttle plate.

He the showed me to spary cleaning down the square hole next to the throttle body throat, that that IAC air passage. Keep spraying cleaner until it runs clear instead of brown.

Also inspect the port where the map sensor hooks up. When my EGR went bad and i was only getting 15 mpg on the highway. All that driving filled the opening with carbon. It was not till a year after the EGR was replaced that I found out about the carbon - the XJ was running poorly.

Install the throttle body with a new gasket, they run around $5.

The first time I had my XJ to the dealer to clean the throttle body I watched the guy do it. Once he had the throttle body back on the engine he hooked up the test set and verified the operation of the engine. He even check the TPS voltage and would of set it if it was wrong. I had used the mulitmeter method and he told me it was not right. He cleaned it an check it over for just 1.0 hour of labor. He even adjusted my throttle body to bring my idle from 1500 to 850 with the transmission in park.

You may want to swing by your dealer or a garage you like and ask them what they use to clean throttle bodies. Make sure you do not spray cleaning on the IAC or TPS. The cleaner could mess up those items.

Before you jump into cleaning the intake manifold do a little test. Hook up a vacuum gauge to the intake manifold. If the vacuum is 16 in Hg or greater you are fine. If the vacuum is 12-13 in Hg at idle then consider cleaning the intake.

My dealer offers intake manifold cleaning as part of the fuel injector cleaning. I seem to recall there is a foam they introduce to the intake, you let it set then run the engine. Suckes the junk through then engine and burns it. You may want to ask the parts guys about the foaming intake cleaner.

Posting-back with results, as requested . . . . . my mechanic installed a used computer and repaired a broken wire and it's running fine again. Don