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Help, have been wrestling with too high idle speed on my 1999 base 9-3 with Turbo and 219,000 miles. This post is a bit long, but trying to provide as much detail as I can to help with recommendations.
For some months I have had the idle speed too high, upon starting it has been about 1500 rpm. When shift to neutral at a stop, again goes to about 1500 rpm. Of course this makes it harder to brake the car. Have been getting engine codes p0507 (idle speed too high) and p1171 (fuel mixture too lean) leading me to suspect vacuum leak. Also have been getting really bad gas mileage, 16-17 mpg for a while, probably due to high idle speed? So I have tried the various approaches:
Cleaned throttle body thoroughly from above and below.
Cleaned original IAC valve carefully per procedures here, no improvement. Purchased a new one (seems to be Chinese model for $33 from Ebay), but no real improvement with new one.
Checked as carefully as I could for vacuum leaks. Sprayed many areas and hoses with carb cleaner trying to see if I could detect rise in rpm, but couldn't. (Perhaps because the baseline rpm has been too high to get much of a noticeable increase.)
Replaced vac line from TB to fuel pressure regulator, it definitely needed replacement. Also replaced vac line to charge air bypass valve on turbo, that one was stiffer than needed to be.
A month ago I checked the PCV valve operation - I plugged off vac line between PCV valve and crankcase, and engine rpm decreased significantly, and almost died. Happy that this might be the culprit, I replaced with new PCV valve, however idle remained high, and then when I sealed off same vacuum line with new PCV valve, there was no decrease in rpm, which left me baffled.
Some time ago (30,000 miles ago, before the idle was ever an issue) I replaced the evap purge valve and vac lines to it because it was making a clicking/clacking noise, and it has been quiet ever since.
Car has proper NGK plugs, gapped, installed about 15,000 miles ago. I've looked at the accelerator cables to throttle body, I don't see anything wrong such as binding cables that don't let butterfly valve in TB close fully...
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So after weeks of experimenting and head-scratching symptoms, I have had numerous times very recently where idle upon starting would be 2000 rpm, ranging up to 2500 rpm.
Now after much playing, the idle upon starting is 900 rpm, but when warms up goes to 1500 rpm when in neutral at a stop light etc.
So today I tried various tests, with the following results:
when I disconnect vac hose to charge air bypass valve, rpm goes up 200 rpm.
when I put my finger over vacuum line between PCV valve and crankcase (sequence is TB, hose, PCV valve, hose and then my finger), I feel noticeable suction on my finger, and rpm decreases slightly. But engine does not almost die such as happened when I did that with old PCV valve. What does that mean, does new PCV valve sound like it is ok?
The 1 inch hose to IAC is too thick for me to reliably pinch off, so to test it, first I disconnected electrical harness to IAC, and rpm dropped ~200 rpm and engine ran a little rougher. Then I restored electrical connector, and opened up tubing between IAC and throttle body. I completely sealed off port to TB, but saw no change in engine rpm, still around 900. While doing this, I left open hose leading to IAC, should I have sealed this off as well?
I pinched off the other vac hoses, no effect, except when I squeezed shut the small one to the Manifold Air Pressure (MAP) Sensor on strut, then engine dies completely.
When I disconnect electrical connector to evap purge valve, no change, also no change when I pinch off the larger vac hose to EPV.
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Help, what should I try next? What could be causing the higher idle, especially when warm and in neutral? Could there be other vacuum leaks, such as for the brake booster system which I could test somehow, I am quite unfamiliar with the brake booster system, or valves in it. Also I only checked reliably for vac leaks up to the hard piping for the turbo, but after the charge air bypass valve I wasn't sure how to check beyond that. Can the charge air bypass valve be tested for proper operation?
Could there be other sensor issues, or even ECU problems which could account for this? Are there other factors that I am missing?
posted by 108.31.181...
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