Unfortunately I find myself back on the forums again as I have been pulling my hair out once again with an issue that I can't seem to make sense of. A few months ago my 4.0L V8 98 P38 started idling erratically whereby it would start fine but within about a second the idle speed was around 2500rpm, I could then turn it off, start it back up and then it seemed to go back to normal. I didn't think much of it and simply put it down to yet another "quirk" of the car, jump forward to present day and it has become significantly worse. Now the problems range from starting it and within a few seconds the revs will slowly drop down and then the car will just cut out to starting and again climbing to around 2500rpm. So at the moment I seem to be able to get both a high and low idle speed sometimes 1 start after another.
Some of you may have seen from a previous post that I was having a problem previously with an oil leak. This I seemed to have resolved with the replacement of the valley gasket but I took this as an opportunity to try and resolve my idle speed issue at the same time. As they were coming off as part of the valley gasket change I cleaned the plenum, ram housing, MAF, and throttle body, I also replaced the spark plugs and air filter in the rather vain hope this would fix my problem but sadly not. After doing some more reading up on here a lot of people suggested the possibility of a faulty IACV (or stepper motor whichever you prefer), but as you can probably already tell this also did not resolve the issue.
I have gone round and checked everything that came off and I can't see any obvious air leaks or disconnected plugs. It might be worth mentioning that I noticed a problem with the car shifting between 3rd and 4th it would hesitate to change then drop and raise the RPM when under harsher acceleration, when accelerating normally it seems to shift relatively OK. I did come across another post whereby somebody mentioned similar issues to myself and that his gearbox position sensor was full of water and opening this up, drying it out appeared to resolve the problem but later down he did mention that ignition leads were also changed which may have actually resolved the issue for him.
My question really is has anybody had experience with these sorts of problems or can anybody recommend any potential fix, I think I will probably replace the leads next as I probably should have done this at the same time as the plugs but any help would be greatly appreciated.
Some of you may have seen from a previous post that I was having a problem previously with an oil leak. This I seemed to have resolved with the replacement of the valley gasket but I took this as an opportunity to try and resolve my idle speed issue at the same time. As they were coming off as part of the valley gasket change I cleaned the plenum, ram housing, MAF, and throttle body, I also replaced the spark plugs and air filter in the rather vain hope this would fix my problem but sadly not. After doing some more reading up on here a lot of people suggested the possibility of a faulty IACV (or stepper motor whichever you prefer), but as you can probably already tell this also did not resolve the issue.
I have gone round and checked everything that came off and I can't see any obvious air leaks or disconnected plugs. It might be worth mentioning that I noticed a problem with the car shifting between 3rd and 4th it would hesitate to change then drop and raise the RPM when under harsher acceleration, when accelerating normally it seems to shift relatively OK. I did come across another post whereby somebody mentioned similar issues to myself and that his gearbox position sensor was full of water and opening this up, drying it out appeared to resolve the problem but later down he did mention that ignition leads were also changed which may have actually resolved the issue for him.
My question really is has anybody had experience with these sorts of problems or can anybody recommend any potential fix, I think I will probably replace the leads next as I probably should have done this at the same time as the plugs but any help would be greatly appreciated.
