Hello all! Firstly, sorry for how long this is, and I appreciate anyone's help on this!
I need some diagnostic/troubleshooting help. I drive a 1999 TJ 4.0 w/ auto trans, and after a recent engine replacement (new, zero-mile engine swap) it has developed a small problem that I am playing hell trying to figure out. Right after the rebuild, it was purring better than any previous Jeep I have ever owned. I am absolutely thrilled with how well the whole installation went, but obviously, it wasn’t flawless. Oh, and the new engine has less than 700 miles on it.
The problem: When I start the Jeep it starts right up with no issues. A couple of times in the mornings the RPMs have shot up to almost 2000 and stayed there. Ordinarily, it acts normally. This part of the problem is intermittent. The current weather in my area is about 30 to 35 degrees in the mornings. I shut it down when it decides to do this high idle issue. Then it becomes hard to start after a few attempts. Once it is past being temperamental, it starts up again, and I throw it in gear (forcing the RPMs down) and drive to work. That issue has only happened twice.
Work is 20 miles away, so at highway speeds is when I notice the problem that is plaguing me. I can best describe it as a stutter, but it is slight. While driving, the Jeep will “cough” and the RPMs will dip slightly for a split second then back up to normal. It may do that every minute or so and sometimes a couple of times in a minute’s time frame. It acts like a TPS going bad, but the surging/lagging is much less noticeable than a bad TPS. If I gas it, it seems to respond appropriately.
At city speeds it responds similarly, but less noticeably. When I start from a stop, it lags briefly and almost makes me think it might die, but then immediately starts acting normally.
I can rev the engine at idle and nothing, but if I increase the idle and maintain it, I can get the issue to occur.
I have checked the vacuum lines visually, with propane, and with starter fluid (all at different times) and I cannot get the engine to react so I’m leaning away from the vacuum leak.
Yes, I have searched all over for answers on this forum and all over the net. I cannot seem to find anyone with this issue specifically, and most suggestions are vacuum line checks. I will be grabbing a buddy tomorrow to help me verify that I’m not missing something with the vacuum lines. I expect the same answer.
Lastly, there are no codes whatsoever.
Here is what I have done so far.
I need some diagnostic/troubleshooting help. I drive a 1999 TJ 4.0 w/ auto trans, and after a recent engine replacement (new, zero-mile engine swap) it has developed a small problem that I am playing hell trying to figure out. Right after the rebuild, it was purring better than any previous Jeep I have ever owned. I am absolutely thrilled with how well the whole installation went, but obviously, it wasn’t flawless. Oh, and the new engine has less than 700 miles on it.
The problem: When I start the Jeep it starts right up with no issues. A couple of times in the mornings the RPMs have shot up to almost 2000 and stayed there. Ordinarily, it acts normally. This part of the problem is intermittent. The current weather in my area is about 30 to 35 degrees in the mornings. I shut it down when it decides to do this high idle issue. Then it becomes hard to start after a few attempts. Once it is past being temperamental, it starts up again, and I throw it in gear (forcing the RPMs down) and drive to work. That issue has only happened twice.
Work is 20 miles away, so at highway speeds is when I notice the problem that is plaguing me. I can best describe it as a stutter, but it is slight. While driving, the Jeep will “cough” and the RPMs will dip slightly for a split second then back up to normal. It may do that every minute or so and sometimes a couple of times in a minute’s time frame. It acts like a TPS going bad, but the surging/lagging is much less noticeable than a bad TPS. If I gas it, it seems to respond appropriately.
At city speeds it responds similarly, but less noticeably. When I start from a stop, it lags briefly and almost makes me think it might die, but then immediately starts acting normally.
I can rev the engine at idle and nothing, but if I increase the idle and maintain it, I can get the issue to occur.
I have checked the vacuum lines visually, with propane, and with starter fluid (all at different times) and I cannot get the engine to react so I’m leaning away from the vacuum leak.
Yes, I have searched all over for answers on this forum and all over the net. I cannot seem to find anyone with this issue specifically, and most suggestions are vacuum line checks. I will be grabbing a buddy tomorrow to help me verify that I’m not missing something with the vacuum lines. I expect the same answer.
Lastly, there are no codes whatsoever.
Here is what I have done so far.
- I just installed a reman’d motor. The motor has all-new internals, nothing was used (only the block and head). It was installed per the service manual specs. (the Jeep has 201,000+ miles on it). Yes, everything was put together correctly. We were more than thorough about this.
- New Cam position sensor
- New Crank position sensor
- New Throttle position sensor
- New Intake air temp sensor
- New Plug wires
- New Plugs
- New Water pump
- New Power steering pump
- New Fuel pump
- New O-rings on injectors
- New exhaust header
- New cat-back exhaust
- New coolant hoses
