goldensam

Currently, if I start up my '99 Cherokee Sport 4.0. It seems to idle fine. If I drive it a couple of miles, the idle increase to 1200-1300. If I then put it in park, the idle gradually starts going up to 2000 and above.

I removed and tested the TPS, and it appears to be fine. I had bought another one thinking that that was the problem, but the new does the same thing (I hope they will take it back). The vehicle is not showing any codes either. I checked for vacuum leaks but did not find any. Is there a particular sensor that would do this? Thanks,

goldensam

I am bumping my own thread since the problem continues. I am getting a po122 code. The TPS had been changed, the IAC had been changed, and I even swapped out the PCM with no solution. The car starts and runs fine but after a while, the idle begins to climb to between 1500 and 2000 rpm. I did not find any vacuum leaks nor any visibly bad wires ( I suppose I could start undoing the harnesses but have been putting that off). Since I have the po122 code, which is low voltage from TPS, does the issue have to be in the wiring at this point. Are there any other things to check? Thanks

goldensam

I wanted to post what the problem was since the information might be useful to others in the future. I brought the car to a mechanic who used a smoke machine to look for vacuum leaks. He saw smoke coming from under the intake manifold and guessed that it was a cracked gasket. He estimated the cost of repair to be about $350, so my son-in-law insisted that he do it instead. Once all the necessay parts were remove to get at the manifold, he discovered that the manifold itself was loose! There was one bolt missing and the others were really just hand tight. It was sort of amazing that the Jeep was running as well as it was.

He could have just tightened everything up and it would probably have solved the problem, but since he had come that far already and we had the new gasket, he went ahead and changed it. The old one was not cracked. We also took advantage of the opportunity to remove and clean the injectors and replace the O-rings. The car runs beautifully now.

I have one question though. Do you think that the mechanic should have seen what the problem was instead of settling on the cracked gasket theory?

Waynerd

Depends on what bolts were missing. The bottom ones to the rear aren't very visible. If I owned a shop maybe I would have checked the bolts before assuming. Especially if I noticed a leak in the gasket area.

freegdr

His diagnosis would of fixed the loose manifold if he replaced the gasket. Which needed to be done from it being loose affecting its seal.

XJRed96

Chances are just tightening the bolts up would have solved the problem for a little while, it likely would have devoloped into a leak down the road. Considering the intake and exhaust manifolds share the same gasket it's under much more stress than many other gasket and you can't fault the mechanic on that one too much because that's not a common problem, old bolts just loosening up. Now had you brought the jeep to him and said you just had a head job done, or an exhaust manifold replaced and he saw smoke coming from that area chances are he would have checked the torque on the bolts first.

Oswalla

Bankers are not the only crooks around ! Maybe he did check and knew loose bolts. Came across another crooked mechanic just last week when my Mom showed me an estimate for $1500 worth of repairs. Went to dealer for normal oil change, checked items myself and not one was needed. I checked the oil that was supposedly changed 2 days before, black and old. They didn't even change the oil. Went back with her to talk to management to tell them that she needed to be refunded, no need to argue with them they knew they been caught.

XJRed96

A dealer has a lot more overhead than most private repair shops, so naturally they have a higher inclination to sell certain services such as power steering fluid flush, Air Induction Cleaning/fuel system cleans, Nitrogen for tires, Or selling maintenance services based strictly on time with no consideration for mileage. But they are using OE parts, Often offer a nice waiting room with free coffee, relatively quick service with no appt. A loaner if it can't be done quick. You got a lot of extras at a dealer that you dont get at a private shop.(not a franchise).

And on the subject of the Oil discoloration, I'd be very surprised if they didn't change the oil, If the oil was dark and discolored as you say that means it was dark and discolored before hand and it will take multiple oil changes in rapid succession and maybe even some type of detergent to clean the oil enough where it wont be discolored in 2 days. Draining the oil from the plug gets a lot of oil out of the car, no doubt, but it takes a long time for an engine to drip as much of the oil it can out, and that doesn't include all the little pockets in the head where the oil simply just collects. Once it mixes in with the new oil it looks like it was never changed. Oil appearance shouldn't be your only deciding point.

goldensam

In this case, I am not questioning the guy's integrity. He came highly recommended, and I personally feel that he is trustworthy. He did basically solve the problem, but I was just wondering whether it was reasonable to expect more precision here. I think from the answers posted that most would give him a pass. I figure he made the call when he saw the smoke coming from below the manifold and just went on to the next car; he seems to have a very busy shop. I guess I will give him a "B". Had he nailed it he would deserve an "A". I do want to note that the diagnostic charge was $85., so I was not looking for perfection for free. Thanks for the help.

Oswalla

Just a quick reply. Been playing with autos for over 40 years, I know what old oil looks like, don't need an analysis to tell that. I know personally, mechanics that have quit jobs because of mandated unnecessary work, and they actually had to go to a training course for this.

Not saying all mechanics are like this, just trying to enlighten others that these practices have been around for decades. Wells Fargo just a recent example.

To the OP, I have retorqued those manifold bolts 2 times on my 90' over the years, loose both times. Idle gets crappy in my experience with this issue.

goldensam

Yes, it would seem that re-torquing manifold bolts will need to be added to some sort of maintenance schedule. In my case, since the car is really only driven about 5000 miles a year at present, it can be quite a ways off I hope.

tacklebox

Thanks for the follow up!