QuestionQUESTION: I have a 99LHS 3.5 with 162,000 miles with an intermittent issue:
At idle whether in gear or not the idle will oscillate 200-300 rpm every 5 seconds or so, although it has gone as high as 1,500rpm.
Frequently along with that it will stumble for a second and die. It always restarts fine. There are no trouble codes.
Sometimes it will run fine for days but will suddenly reappear.
My local dealer has looked at it, and fortunately it had the issue at the time. They had the computer connected while it was doing this and everything is operating properly, including the idle air control motor.
They cleaned the throttle body but the issue persists, they are baffled as to the cause.
The last few days the issue has become worse, it has the same symptoms while on the road, not just at idle- accelerating, steady speed and coasting.
Hopefully you can shed light on this puzzle.
Thank you
ANSWER: Hi Mike,
Stalling with no fault codes and even with the diagnostic readout box connected suggests it is some sort of a problem with a part that is not well-monitored. My only suggestion would be that you examine the exhaust gas recirculation valve which can impact the idle misture and accelerating performance when it is necessary for the that valve to be firmly closed. It builds up exhaust crud and the valve stem may get sticky and fail to close all the way even thought there is internal spring-action that tries to close it. I'm not certain that the valve stem is 'external' so it can be moved back and forth and observed. If not then removing the valve and cleasning out the exhaust passageway and spraying some WD-40 internally for lubrication of the valve/stem may solve this problem. If the valve stem is visible you can look for a slot into which the tip of a screwdriver can be inserted to allow you to check its action and to spray WD-40 on the stem where it enters the body of the valve. The valve is located toward the rear of the engine underneath the throttle body and you will need to remove the pipes that attach it to the engine to check it out internally.
Please 'rate' my answer (see the PS below). Sorry for the delay but I just found your question in the pool to which it had been referred by Kevin.
Thanks,
Roland
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QUESTION: Roland,
Thank you very much for your quick response. The EGR had occured to me but I assumed I would have gotten an EGR related trouble code. Can your suggestion occur without tripping a trouble code?
I have also noticed a drop in gas mileage, does this tie in with your diagnosis?
Thank you
ANSWER: Hi Mike,
The 5 fault codes for the egr measure whether or not it moves, basically, when tested. I am not expert enough to be certain that my diagnosis is correct of course, nor have a experienced any one of those trouble codes to know what will set them. But I would suspect that a valve whose stem or valve seat is gummed up near the fully closed position will still move in response to being tested but not set a fault code when it is just slightly ajar and allowing exhaust gas to enter the manifold and dilute the mixture to a level which causes stalling or reduced gas mileage as the result. It is a common occurence in my experience but I haven't learned of these trouble codes being 'called out' with similar frequency.
The '98 manual lists the step for egr removal to include taking of the tubes that connect it to the intake manifold (which is a bit more than I would want to do because of the need to remove the intake plenum and fuel rail) but the '04 manual with the same basic figure of the set up says that only the 4 screws at the egr valve itself needs to be removed (and that looks straightforward). So have a look and see if the latter is correct. It would be worth the effort were that all that needs to be done to inspect it. Also, examine the valve as it sits to see whether the valve stem is accessible to spray with WD-40. Please let me know what you learn.
Please 'rate' my answer (see the PS below).
Thanks,
Roland
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QUESTION: Roland,
Thanks for your additional response. I am planning on calling my dealer tomorrow and discuss with them again, however there is something I realized I did not make clear. When I indicated the issue is intermittent, it may run fine for a day or few days, but once it starts it keeps doing it every 10-15 seconds as long as I am driving.
Does this provide any additional clue?
As I mentioned for a few weeks this only occured at idle but now occurs through all ranges.
Thank you again.
AnswerHi Mike,
If it is occuring all the time once it starts and does it every 10-15 seconds and at various throttle positions/accelerating/coasting/cruising/slowing down... then that would make me think of an electrical intermittent. Have you tried the self-diagnostic readout: On-off-on-off-on and leave on with the ignition key and doing that in 5 seconds or less elapased tiem? Watch the odometer window to see if the mileage reading is replaced by any 4-digit numbers preceded by a P. Let me know if so, otherewise my thought is one of the circuits powered out of the ignition switch may be flaky.
Please 'rate' my answer and consider giving me a 'vote' for 'volunteer of the month'.
Thanks,
Roland
