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Old 07-05-2011, 01:23 PM   #1
canyonman
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Default 2002 Idle speed and stalling issues

I have a 2002 sl2 145k miles with manual trans. Problem started with an intermittent high idle at start up followed with a very low idle or stall when the clutch was pressed this gradually got worse to where the car would not idle at all. I should mention the car is not setting any codes. At other times the car would run as if nothing was wrong.
The repairs made so far: because of different DTCs set before emissions testing the EGR, TPS, IACV, and ECT sensor were all replaced about one year ago. At that time this problem was not occurring.
I replaced the IACV again last week and for 300 or so miles the car ran like a top. Now the last two mornings when I start the car it revs up to about 3k rpm settles down to sub 1k rpm and bounces up and down. When you take off to drive, it drives fine until you step on the clutch then it drops to 500 rpm or stalls. This will go on for 10 miles or so then it straightens out and drives fine. Iím stumped at this point.
I should also mention that with the IACV completely closed the engine would not idle at all, I cleaned the TB thoroughly and had to adjust the throttle plate for a 500 rpm idle with no IACV input.
Any ideas on where I should look next?
I have used a friendís actron scanner to read live sensor data but admittedly don't really know what Iím looking for.

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Old 07-06-2011, 10:31 PM   #2
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Default Re: 2002 Idle speed and stalling issues

Nothing??? Beuller? Bueller?

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Old 07-06-2011, 10:54 PM   #3
ehunter
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Location: Pacifica by San Francisco Ė 5sp Ė Engine rebuild with the help of people here at 177K due to 500mi/qt oil consumption. After 2yrs I am back to 40mpg+ after discovering the refirb head I used was bad. Car runs better than a top. Now at 205k.
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1996 SL2
Default Re: 2002 Idle speed and stalling issues

Intake manifold vacuum leak?

Try spraying brake cleaner all over the inlets, junctions of the intake manifold. If the high/low idle goes away you will know where the problem is centered.

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Old 07-07-2011, 12:03 AM   #4
td1238
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Default Re: 2002 Idle speed and stalling issues

I cannot see an intake manifold having an intermittent leak like this that would both cause a high idle at start-up and also a stall condition later.

Still it's worth a try.

I'd more likely look at the TPS or IAC again, or possibly the MAP sensor or something like that.

If your friend's scanner has a 'view data' section, take a look there. Watch the TPS as it is opened. Numbers should start at 0, climb smoothly (not jump up and down while throttle is being moved in one direction only), and return to 0 when throttle is closed.

An intermittent or worn TPS can cause all sorts of trouble. Just unplugging it under various conditions can duplicate some of these troubles. Make sure that the plug is connecting properly, too. Wiggle it and the wires connecting and watch for changes.

Perhaps the IAC is sticking?

Possibly, though not extremely likely, since the car will often idle fairly well without it, the MAP sensor might be malfunctioning. With the key on and engine off the reading should be near 100, and should correspond to local barometric pressure. At idle it should read in the 20s, and the reading should increase as the load on the engine is increased (increased throttle, climbing a hill, etc.). Readings with engine running should correspond to actual manifold vacuum according to the following chart: http://www.aa1car.com/library/map_sensors.htm Initial barometric pressure reading should likewise correspond to the chart.

If the MAP sensor were to malfunction, the computer might not be able to compensate fuel and timing, and possibly speed, for changes in load. This might definitely be the case if the clutch were let out fairly quickly, and possibly even slowly. Without accurate MAP sensor readings, the computer would not be able to accurately predict the change in load.

Last edited by td1238; 07-07-2011 at 12:06 AM.. Reason: Added info.

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Old 07-07-2011, 12:10 AM   #5
td1238
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Default Re: 2002 Idle speed and stalling issues

You can also check a TPS and MAP sensor with an ohmmeter and volt meter respectively, if a scan tool with the 'view data' feature is not available.

An ohmmeter measures between the TPS center terminal, and each of its outer terminals, one at a time. Watch for jumping around and not starting and stopping in the same place each time.

The MAP sensor voltage is read between the center terminal and the ground terminal. The voltage should be close to 5 with the engine off, key on, and should fall down to around 1 at idle. All voltages read should correspond to the chart listed previously, and to actual manifold vacuum readings taken with a vacuum gauge. A vacuum pump with accompanying gauge can also be connected directly to the MAP sensor vacuum nipple to simulate the entire range of vacuum conditions that the engine will encounter while in operation.

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Old 07-11-2011, 08:16 AM   #6
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Default Re: 2002 Idle speed and stalling issues

Thanks TD1238 for the info on the MAP sensor readings, MAP proved to be ok.
Had already checked for vacuum leaks there were none. By chance was able to "fix" it temporarly by unplugging the IAC valve then plugging back in so started to suspect the connector. Located a replacement and installed, so far so good. I cannot see anything wrong with the original connector even tried to bend the sockets a little for a little more tension with out any luck.
Thanks again for the help.

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