1996 Chevy Lumina- High Idle Problem

Scottedawg

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#1
Hello All,

I have a 1996 Chevy Lumina, 3. 1 V-6, 120,000 miles. I have an error code of P0507 that keeps popping up.
My engine idles great at times but sometimes idles at 1,000 to 1,200 rpm. Usually happens when I stop at a light. Sometimes when I take off the car takes off on it's own without touching the gas. Other times it runs great. I replaced the IAC valve (twice), cleaned the EGR valve and replaced the EGR valve gasket. Within the last three months I have replaced the TPS sensor, the MAF sensor, the fuel pressure regulator and replaced all the vacuum lines with new ones. The PCV valve is clean and operating properly also. Everything else on the car runs great and there are no coolant leaks. I would appreciate any ideas that you all have on this problem.

Thanks in advance.

Scottedawg
 

Gus

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#3
If you have access to a scan tool, look at the TPS and IAC data.....tps should be 0 %(if higher, then thottle plate could be stuck open, like Jim said).......IAC should be 15-20 counts....if much higher, then sensor/ECM problem....if it reads "0" counts, you have a vacuum leak...
 

Scottedawg

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#4
Jim and Gus, Many thanks for the great advice. I checked on my throttle linkage
and it appears to be operating properly. The throttle plate is clean and appears to be
closing and opening without difficulty. I do have a "ACTRON" scan tool, but it
doesn't have IAC and TPS data included on it. It reads as follows.

RPM 947.
Load value 2. 7%.
Air Flow Rate 4. 71 Gr/Sec.
MAP Sensor 35 KPA.
Coolant 201 F.
Short Term Fuel Trim 1 -3. 4%.
Long Term Fuel Trim 1 -2. 2%.
Short Term Fuel Trim 3 -72. 9%.
Long Term Fuel Trim 3 36. 2%.
EGR System Monitor O. K.

Any further ideas or advice from this point would be appreciated. Thanks again. . .

Scottedawg
 

tduty

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#6
hey scott
this might be the problem, cable strands broke in throttle cable, i've seen this on lifttrucks with throttle bodies and it doe's same intermittent issue or vacuum leak where throttle body bolts to intake rot's o' ruck tim
 
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#7
Scottedawg said:
Jim and Gus, Many thanks for the great advice. I checked on my throttle linkage
and it appears to be operating properly. The throttle plate is clean and appears to be
closing and opening without difficulty. I do have a "ACTRON" scan tool, but it
doesn't have IAC and TPS data included on it. It reads as follows.

RPM 947.
Load value 2. 7%.
Air Flow Rate 4. 71 Gr/Sec.
MAP Sensor 35 KPA.
Coolant 201 F.
Short Term Fuel Trim 1 -3. 4%.
Long Term Fuel Trim 1 -2. 2%.
Short Term Fuel Trim 3 -72. 9%.
Long Term Fuel Trim 3 36. 2%.
EGR System Monitor O. K.

Any further ideas or advice from this point would be appreciated. Thanks again. . .

Scottedawg
Your data doesn't make much sense. What is the Short and long term FT 3? Is this a typo? Should this be stft2?
Bank 2 is the back bank and according to this data it's taking away a lot of fuel short term and adding it considerably for the long term.
Recheck with a different scan tool. If that tool you have doesn't support IAC, TPS etc. you should consider a different tool.
 

Scottedawg

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#8
I checked my engine vacuum and it is 18 Hg steady at idle, engine warmed up, with no
fluctuation of the needle at idle. All vacuum lines were replaced about two months ago.

I thought the throttle body gasket may be the culprit so I sprayed carb cleaner while the
engine was running around intake gasket and throttle body gasket to check for possible
vacuum leak, and there was no fluctuation of engine speed during this test. So the
throttle body and intake gasket appear to be OK. Is there something else I can do to
check those gaskets?

I also re-checked the data from my scan tool and it is STFT 1, LTFT 1, STFT 3 and LTFT 3.

Thanx,

Dawg
 
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#9
Scottedawg said:
I checked my engine vacuum and it is 18 Hg steady at idle, engine warmed up, with no
fluctuation of the needle at idle. All vacuum lines were replaced about two months ago.

I thought the throttle body gasket may be the culprit so I sprayed carb cleaner while the
engine was running around intake gasket and throttle body gasket to check for possible
vacuum leak, and there was no fluctuation of engine speed during this test. So the
throttle body and intake gasket appear to be OK. Is there something else I can do to
check those gaskets?

I also re-checked the data from my scan tool and it is STFT 1, LTFT 1, STFT 3 and LTFT 3.

Thanx,

Dawg
You should get the vehicle to someone who has a scan tool that will give you adaquate info. That engine doesn't have three banks and you can't depend on much of what it's telling you. You need a tool that will give you real time reading of the IAC while using a graphing meter to verify what's actually happening at the valve. You may have a simple wiring problem, pin tension or corrosion. Check pins 9-12 at the connector of the PCM.
 

Scottedawg

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#10
Well . . It wound up being my transmission after all the trouble shooting. The 1-2 switch went completely out and put the car in Limp mode. So I had to bite
the bullet and spend around $1000. 00 to get it fixed at a chevy garage. It was too much of a job for me to do. Anyway I want to thank all of you for the
advise and I will continue to support BAT Auto . . . Hope you all have a Great New Year . . . Scott E Dawg
 

Gus

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#11
You never said you had a problem with the vehicle shifting through the gears? "Everything on the car runs great."