94 4.0 throttle & idle problems
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94 4.0 throttle & idle problems
I have a 94 4.0L XLT that is having problems idling and is doing some weird stuff while driving. In Park or Neutral the engine will idle fine one minute and then automatically lower rpms until it is just at the point right before stalling. It will sit there and then rev up to normal ~800rpm. While driving, sometimes I will push on the accelerator and I will get very little acceleration, then about 15-30 seconds later I will get a burst of throttle, like it just decided to finally give it gas. I replaced and cleaned the parts listed below and I am still stumped.
1. TPS = replaced
2. FPR = replaced
3. IAC = cleaned
4. MAF = cleaned
5. spark plugs = changed
I would appreciate the help.
Dave
1. TPS = replaced
2. FPR = replaced
3. IAC = cleaned
4. MAF = cleaned
5. spark plugs = changed
I would appreciate the help.
Dave
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Joined: Aug 2002
Posts: 12,679
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From: BC, Canada
94 4.0 throttle & idle problems
Hi dhpweingardt and welcome to FTE 
Have you checked for vacuum leaks? The most common place is where the upper intake manifold attaches to the fuel rail and where the fuel rail atttaches to the lower intake. You can check for a leak with some spray carb cleaner such as Carb Medic.
With the engine idling you spray the carb cleaner at the area where you suspect a leak and if the idle either drops or raises when the carb cleaner hits it you've found your leak.
Let us know how you make out.
Have you checked for vacuum leaks? The most common place is where the upper intake manifold attaches to the fuel rail and where the fuel rail atttaches to the lower intake. You can check for a leak with some spray carb cleaner such as Carb Medic.
With the engine idling you spray the carb cleaner at the area where you suspect a leak and if the idle either drops or raises when the carb cleaner hits it you've found your leak.
Let us know how you make out.
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94 4.0 throttle & idle problems
I just finished doing a valve job and I replaced those gaskets. I'm suspecting a vacuum hose I may have missed, but I just haven't been able to find it yet. Do you think the Carb cleaner technique would work on a broad basis? (start on each side of the car and spray locations) I appreciate the help and keep the good suggestions coming. I am also heading to Kragen tomorrow to pick up a code reader.
Thanks again,
Dave
Thanks again,
Dave
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94 4.0 throttle & idle problems
Ok, I pulled the codes and got a '542'
The book states it is a "fuel pump secondary circuit failure, PCM to Ground"
I think I may have pinched a wire when I put back the sending unit when I replaced the float. (was done on the same repair as the valve seals). I'll write more when I get a chance to pull the tank.
Dave
The book states it is a "fuel pump secondary circuit failure, PCM to Ground"
I think I may have pinched a wire when I put back the sending unit when I replaced the float. (was done on the same repair as the valve seals). I'll write more when I get a chance to pull the tank.
Dave
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94 4.0 throttle & idle problems
No raceruy, it did not run like this before I did the valve seals.
I did a search on code 542 in the forum and found a thread back in 2000 called "Once warmed up" and he seemed to have the same problem, but no fix was documented.
Dave
I did a search on code 542 in the forum and found a thread back in 2000 called "Once warmed up" and he seemed to have the same problem, but no fix was documented.
Dave
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Joined: Aug 2002
Posts: 12,679
Likes: 15
From: BC, Canada
94 4.0 throttle & idle problems
I would clear that code and see if it comes back. I've seen fuel pump codes when there didnt seem to be anything wrong and once they were cleared they never came back.
Seeing that it ran ok before you did the heads I would sure double check everything. It still sounds to me like a vacuum leak or a couple vacuum hoses on wrong or something like that. Or possibly a wire off somewhere. It's been a while since I've had an older 4.0L apart and I cant think of any common wires that would cause a problem. Maybe a ground wire off somewhere? TPS is plugged in ok? No leaks between the MAF and the intake? Does it run smooth after the inital problem or does it miss? I've seen plug wires put on wrong on these as they dont go on in order on the coil pack.
I cant think of anything else right now.....had a tiring day at work
Seeing that it ran ok before you did the heads I would sure double check everything. It still sounds to me like a vacuum leak or a couple vacuum hoses on wrong or something like that. Or possibly a wire off somewhere. It's been a while since I've had an older 4.0L apart and I cant think of any common wires that would cause a problem. Maybe a ground wire off somewhere? TPS is plugged in ok? No leaks between the MAF and the intake? Does it run smooth after the inital problem or does it miss? I've seen plug wires put on wrong on these as they dont go on in order on the coil pack.
I cant think of anything else right now.....had a tiring day at work
