GM '165 ECM with 12P - high idle, wont drop

American Delco GM ECUs and PCMs, ALDL, OBD 1.5.
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GM '165 ECM with 12P - high idle, wont drop

Postby Mark_ZZ3 » Thu May 12, 2022 1:46 pm

Trying to solve a higher than normal idle. When engine is warm idle goes higher than commanded idle. Looking for 1100, but it revs at 1500, and climbs to 2000 at times. IAC is around 75-80 and does not go down to reduce rpm (maybe outside of idle zone?). I would expect to see IAC drop down to zero trying to lower RPM ... but seems to say around 70's.

As it was warming up, it behaves more typical. Idle around 1100, map at 45 kpa. When engine is hot, RPMs are much higher ... thinking I am missing a config item somewhere.

No vacuum leaks and can stall engine if you plug air inlet. Timing is accurate from Tunerpro vs. timing light. Fueling is OK. Replaced the IAC and TPS. Plugs, wires, cap all new.

Is there something in 12P code I am missing for Idle parameters? Can't seem to find any reason why idle would climb. How can I get IAC to drop down?

... The engine is a 4 cyl with TBI injection, induction pickup. This config ran will last year on a 2.5L, but this year on a 3.0L ... some issues to iron out.

Mark.

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Re: GM '165 ECM with 12P - high idle, wont drop

Postby Mark_ZZ3 » Thu May 12, 2022 2:07 pm

Scanning logs ... the only item I can find in one case, the MAT sensor was unplugged which then reads -36 or something. I could see this cause a fueling issue ... but should not be high idle?

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Re: GM '165 ECM with 12P - high idle, wont drop

Postby antus » Thu May 12, 2022 5:29 pm

Ive had a look at your logs in the other thread. You fuelling seems very rich at idle. Your short term integrator is -7 in places to inject less fuel based on what the VE is requesting, and yet the O2 is still beyond the limit of the sensor rich. I think you need to tune your idle area VE better, then revisit cold engine correction if you need to for startup. If you are having trouble with idle you should verify your injector opening times versus voltage are correct for your injectors. If you bake in an offset to the VE table for this you'll get wildly different fuelling between hot and cold because of small changes to the opening time making more or less difference than they should.
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Re: GM '165 ECM with 12P - high idle, wont drop

Postby Mark_ZZ3 » Thu May 12, 2022 10:58 pm

antus wrote:Ive had a look at your logs in the other thread. You fuelling seems very rich at idle. Your short term integrator is -7 in places to inject less fuel based on what the VE is requesting, and yet the O2 is still beyond the limit of the sensor rich. I think you need to tune your idle area VE better, then revisit cold engine correction if you need to for startup. If you are having trouble with idle you should verify your injector opening times versus voltage are correct for your injectors. If you bake in an offset to the VE table for this you'll get wildly different fuelling between hot and cold because of small changes to the opening time making more or less difference than they should.


Thanks.

The injector and offset are same as previous setup ... so I never gave them a second thought. I do know in once test the alternator wasn't working and fueling was way off thus supporting your statement the inj offsets are wrong.

The challenge is that I remember it worked and we only changed one small thing ... the engine! :-)

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Re: GM '165 ECM with 12P - high idle, wont drop

Postby kojab » Fri May 13, 2022 10:44 am

Check your TPS closed throttle Voltage. Should be around 0.7V - 0.8V approx. Typically it is less than 1 Volt.

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Re: GM '165 ECM with 12P - high idle, wont drop

Postby Mark_ZZ3 » Fri May 13, 2022 2:41 pm

kojab wrote:Check your TPS closed throttle Voltage. Should be around 0.7V - 0.8V approx. Typically it is less than 1 Volt.


I set it to .25V. Anything higher the TPS % value was above 0. Seems like the lowest this could be. If I had .7V, the % woold be 10% open I'd guess.

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Re: GM '165 ECM with 12P - high idle, wont drop

Postby kojab » Sat May 14, 2022 7:58 am

Just set the closed TPS voltage to 0.7V making sure you are using the same earth as the PCM D2 . After starting the engine or cycling the IGN key the TPS voltage should automatically read 0%

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