Idle issues getting worse. Thoughts?
06-06-2005, 03:51 AM
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Idle issues getting worse. Thoughts?
This is on the 951. . .
When the car is cold it idles like crap. Occasional misfiring and the boost level to maintain idle is about 0.6 or even as much as 0.7 bar at times. Once the car warms up, it's smooth and runs well although the idle RPM will occasionally creep up from normal to about 1,200 RPM or so. The latter problem has existed for a while and I suspected it was a bad or dying ISV, the former problem is more recent (within the last couple of weeks) but progressively getting worse. Any thoughts?
I was going to pull the plugs and check for fouling, but anything else it could be? Plugs, cap & rotor, ISV?
When the car is cold it idles like crap. Occasional misfiring and the boost level to maintain idle is about 0.6 or even as much as 0.7 bar at times. Once the car warms up, it's smooth and runs well although the idle RPM will occasionally creep up from normal to about 1,200 RPM or so. The latter problem has existed for a while and I suspected it was a bad or dying ISV, the former problem is more recent (within the last couple of weeks) but progressively getting worse. Any thoughts?
I was going to pull the plugs and check for fouling, but anything else it could be? Plugs, cap & rotor, ISV?
06-06-2005, 12:09 PM
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I'm sure you have probably already checked this, but when I was having the same problem, it turned out to be a vac leak. When the car warmed up, it wasn't as bad. Have you tested the ISV? I prefer to make bungs rather that jumper the diag port, because I have heard of issues where the ISV housing will actually leak a little.
06-06-2005, 02:52 PM
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"Once the car warms up, it's smooth and runs well although the idle RPM will occasionally creep up from normal to about 1,200 RPM or so."
Yeah, most likely a leak. The major factor that determines idle-speed is air-volume. In order to idle at 1200rpm, you have to be sucking in sufficient CFM in order support that engine speed. The DME uses the ISV to force an 840rpm idle-speed, you can try adjusting the throttle-bypass screw in a properly working car and you'll see that idle-speed won't change at all because the DME is adjusting the ISV in the opposite direction.
Most likely in your car, the ISV is fully closed already (DME's tried all it can to reduce idle speed) and you're still getting 400rpms too-high of an idle. That's about 50% more air than required for idle. Most likely due to a leak after the throttle-body somewhere. This causes cold-starts to be way too lean because the computer injects a fixed amount of fuel because it assumes a stock amount of idle air, not the 50% extra that you have, thus resulting in a lean mixture that causes the stumbling and dying car. The O2-sensor isn't warmed up yet, so you don't get auto-correcton function to add more fuel. When the car and O2-sensor is warmed up, it adds extra fuel to compensate for the leak and the idle increases due to the more optimum combustion.
What's your intake-manifold vacuum at idle when the car's warmed up? Use an aftermarket gauge T'd off the KLR's manifold-pressure line.
Yeah, most likely a leak. The major factor that determines idle-speed is air-volume. In order to idle at 1200rpm, you have to be sucking in sufficient CFM in order support that engine speed. The DME uses the ISV to force an 840rpm idle-speed, you can try adjusting the throttle-bypass screw in a properly working car and you'll see that idle-speed won't change at all because the DME is adjusting the ISV in the opposite direction.
Most likely in your car, the ISV is fully closed already (DME's tried all it can to reduce idle speed) and you're still getting 400rpms too-high of an idle. That's about 50% more air than required for idle. Most likely due to a leak after the throttle-body somewhere. This causes cold-starts to be way too lean because the computer injects a fixed amount of fuel because it assumes a stock amount of idle air, not the 50% extra that you have, thus resulting in a lean mixture that causes the stumbling and dying car. The O2-sensor isn't warmed up yet, so you don't get auto-correcton function to add more fuel. When the car and O2-sensor is warmed up, it adds extra fuel to compensate for the leak and the idle increases due to the more optimum combustion.
What's your intake-manifold vacuum at idle when the car's warmed up? Use an aftermarket gauge T'd off the KLR's manifold-pressure line.
06-06-2005, 08:41 PM
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Just a shot in the dark here. When was the last time you did anything to or around the fuel injectors? If you were to have a leaky O-ring on the bottom of it, could that not cause a condition somewhat like you describe in the form of a vacumn leak? I just changed out the fuel injectors on both my '83 and my '85/1 avatar car this last weekend. It made a WORLD of difference in how my '83 would start up, idle cold and hot ( I had a fair, hot idle miss to it, but ran out pretty good), and running down the road. The only real indication of a possible leak was kinda of oily/greasy area around # 2 injector. Maybe if you try spraying carb out, or similar to the bottom of the injectors while running, it may tell ya if this may be a cause of concern? WitchHunter charges $12.50 each to clean/flow test these.....a good deal, and he did a mighty fine job. Good luck! 
06-06-2005, 09:02 PM
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OK thanks guys I'll check all that. The injectors were re-sealed (new o-rings & caps) recently but not rebuilt or anything and I put new lindsey tubing in about 5 months ago to replace all the stock stuff. It might be one of the larger hoses though (like the two that go from the ISV to the intake - those were pretty badly hardened / brittle when last I checked. Possible. Maybe the big one off the brake booster as well. Dunno. I'll check and get a vacc. reading in any case. Thanks guys.