High idle troubleshooting

[Trstno1]

Ok guys.

I have just recently installed a DMC stage 1 exhaust. Since before then I had noticed a high idle with my car with a rich mixture. I sort of figured it may have been a plugged cat, which was one of the reasons I replaced my exhaust system. Unfortunately, the problems still exist even after the new exhaust.

When I go to cold start it, it seems to fire immediately but then die if I don't feather the gas pedal. Once it dies, I go to turn the car again and it will turn without fire for about 3-5 seconds, then roar to life. Once it does catch it runs like crap for a couple of seconds and then the idle stabilizes around 1k rpm. Though once I drive it, the idle will never go below 13-15k rpm. I have witnessed the idle throttle micro switch engaged when at idle, I just haven't tested any electrical aspect of the switch.

I have read other high idle threads and tried a couple of things in order to troubleshoot. I have unplugged the throttle control valve, but the idle stayed constant at 13k rpm. I plugged it back in and unplugged the new O2 sensor but with no change in idle as well. it doesn't even appear as thow the lambda system is working at all. Does anyone have any ideas as to how I can make sure the lambda system is working, and or how to get this high idle under control?

Thanks for any ideas in advance.

[Rich]

Let's work on the basics to start with.

You report seeing the idle microswitch being toggled when the engine is supposed to be idling. And then after you drive it a bit the idle goes up to 1300-1500RPM, right?

When it is idling at 1300-1500RPM please report whether the idle microswitch is still engaged. And if the throttle linkage is indeed closed in that condition.

The easy check during high idle is to to manually push the throttle closed at then last point in the linkage. If the idle drops then check your linkage/cable.

When I go to cold start it, it seems to fire immediately but then die if I don't feather the gas pedal. Once it dies, I go to turn the car again and it will turn without fire for about 3-5 seconds, then roar to life. Once it does catch it runs like crap for a couple of seconds and then the idle stabilizes around 1k rpm. Though once I drive it, the idle will never go below 13-15k rpm. I have witnessed the idle throttle micro switch engaged when at idle, I just haven't tested any electrical aspect of the switch.

[Jonathan]

The easy check during high idle is to to manually push the throttle closed at then last point in the linkage. If the idle drops then check your linkage/cable.

Rich is right. First things first. If it's high idling, stop and pull over, get out and push with your finger on the end of the pin that contacts the microswitch tab (backside of the end of the lever arm). You could also try to push down on the microswitch tab with a small screwdriver if by chance the rest screw is adjusted too far in and the actuating pin isn't reaching the microswitch tab because of that.

From my own experiences with high idles, if the idle you are hovering at isn't a fairly specific and consistent number (like 1,200 or 1,300 RPM as you said), it's probably throttle spool/linkage related. If it sits right at 2,000 RPM or 2,500 RPM every time, it's more likely a poor ECU connection somewhere or bad idle speed motor.

[BigBenb84]

I just resolved my high idle problem. Of course eliminate linkage/idle screws/microswitches as the culprit first. I was running too rich. Have you hooked a dwell meter to it? I bought one off eBay and hooked it up. Had to back out the mixture screw a lot till it started to cycle (freq valve buzzing) normally and the idle went back to normal. I have a thread w/video on here about it somewhere (I'm on the app now or else I would give the link).

[Trstno1]

[QUOTE=BigBenb84;174172]I just resolved my high idle problem. Of course eliminate linkage/idle screws/microswitches as the culprit first. I was running too rich. Have you hooked a dwell meter to it? I bought one off eBay and hooked it up. Had to back out the mixture screw a lot till it started to cycle (freq valve buzzing) normally and the idle went back to normal. I have a thread w/video on here about it somewhere (I'm on the app now or else I would give the link).[/QUO

I would be very interested in seeing that video as my car runs rich as well. Could you throw me a link when you get the chance?

Thanks,

[Trstno1]

Ok guys-

I just got around to actually investigating the micro switch only to realize two things. When at idle, the micro switch is being activated. Second, that the PO must have unplugged the micro switch as both spade terminals were unplugged!! I plugged it in and the idle immediately went from 1500 rpm to 1000 rpm just like that. Unfortunately, that's where it idles......1000 rpm. It still seems a bit high. Would there be any reason someone would unplug a micro switch? I did notice that when the car first started with the micro switch plugged in, it ran pretty crappy for a minute with the engine shaking a bit until it warmed up. I'll have to let it cool down again to see if the startup/ warmup behavior will be replicated.

As a side note: though I don't think this is the problem, I did recently installed a DMC type 1 exhaust. It also has a new O2 sensor. Though when running, unplugging the idle control valve or the O2 sensor results in no change to the idle. Is that normal? It still sits at 1k rpm. It also acted the same way prior to the exhaust change.


Second side note: I have always had a problem with the car starting and staying running the first time I turn the key. It will always fire within 1 second with what sounds like a strong start but then immediately die. The second time I turn the key, it will crank a second longer, and it will stumble to life and stay running though running rough. The vibration of the engine will shake the car. However, onece it warms up for about a minute the vibration goes away and the car seem to run fine for the most part. I have tried all conceivable combinations of babying the accelerator before the first start to keep it running the first time but very rarely can I get the timing just right to do so. What could that issue be? Fuel pressure? It still has the stock fuel pump setup. ( one of the only things I haven't replaced yet). Does the stock setup have a fuel check valve to keep the system pressurized?

Third side note: once the car has been running for awhile or has been driven, it will always hot start the first time and stay running without exception.


Anyone have any suggestions as to what my next step would be? Test the dwell? Put a check valve in for the fuel pressure? I would really like to get my car to start the first time, stay running, and idle normal.

Any suggestions would be greatly appreciated.

[Bitsyncmaster]

Unless you have my idle ECU, with the idle switch disconnected and engine warm you will get ignition advance and high, crappy idle.

You should be at 775 RPM idle speed. Try backing out the curb (lower) screw. You may have to also adjust the idle switch screw if you move the curb idle screw much.

Mixture adjustment is critical to get good cold engine running good. A lot of people just adjust it for best idle and that makes it way off.

Does your fuel pump prime (run for a second) when you just turn the key from off to on?

[Trstno1]

Unless you have my idle ECU, with the idle switch disconnected and engine warm you will get ignition advance and high, crappy idle.

You should be at 775 RPM idle speed. Try backing out the curb (lower) screw. You may have to also adjust the idle switch screw if you move the curb idle screw much.

Mixture adjustment is critical to get good cold engine running good. A lot of people just adjust it for best idle and that makes it way off.

Does your fuel pump prime (run for a second) when you just turn the key from off to on?

Yes the fuel pump primes. I can hear it when I turn the ignition on prior to crank. However, it doesn't matter if I wait for the cycle to complete or not....it still dies directly after cold startup. Is the curb screw the lower screw on the the micro switch bracket? Sorry I'm still a newbie...

[Bitsyncmaster]

Is the curb screw the lower screw on the the micro switch bracket? Sorry I'm still a newbie...

Yes

[DMC5180]

Just ensure the lower adjusting screw is not contacting the bracket (throttle plates closed) and make sure the upper screw still triggers the micro-switch.

Your cold start issue could be attributed to a leaking injector. The next time your do a cold start try pressing down on the the gas pedal a little after it the engine fires. See if that clears the initial rough idle then let off the pedal to see if the idle is stable @ 775 +- 25.