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V6 Discussion and questions about the base carbureted or MPFI V6's and the rare SFI Turbo V6.

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Old 04-18-2011, 03:56 AM   #1
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Join Date: Apr 2011
Location: West Virginia
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Car: 1988 Firebird
Engine: 2.8 MPFI V6
Transmission: 700R4 Auto
Axle/Gears: 10 Bolt, 3.42 Std

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Check Engine Light/High Idle..HELP!!

I noticed here about a month and a half ago that my 2.8 MPFI V6 was idling at a very high rate (about 1800RPM at start up and climbs to 2600RPM during warm up). I've done everything I can think of to get it to come back down. I've replaced the TPS, even adjusted it down to the lowest setting to see if that would work. Still nothing is happening. Now my check engine light is on. It's throwing a code 12 meaning no distributor reference pulse, or the tach is not reading right. I've replaced the distributor cap, rotor, ignition module, plugs and wires. Still nothing is helping. What do I do to fix this problem? The only thing I can think of doing is replace either the pick-up coil or the whole damn distributor. Any advice?
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Old 04-18-2011, 10:48 AM   #2
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Re: Check Engine Light/High Idle..HELP!!

Code 12 can be ignored every time you check for codes it will always flash code 12, it will do so 3 times and then it will give you another code or codes if the check engine light is on. Check your IAC valve to see if there is carbon build up where the valve opens and closes to adjust idle. Also your TPS needs to be set at .54 volts anything else and it will more than likely idle funny. Check for vacuum leaks also as they are usually the culprit for high idle.
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Old 04-18-2011, 07:31 PM   #3
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Re: Check Engine Light/High Idle..HELP!!

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Originally Posted by firebird904 View Post
Code 12 can be ignored every time you check for codes it will always flash code 12, it will do so 3 times and then it will give you another code or codes if the check engine light is on. Check your IAC valve to see if there is carbon build up where the valve opens and closes to adjust idle. Also your TPS needs to be set at .54 volts anything else and it will more than likely idle funny. Check for vacuum leaks also as they are usually the culprit for high idle.
.. are carb'd cars the same advice, like on my 1984?

Check Engine light hasnt come on in awhile. Bu it used to, intermittently.. now i cleaned out engine carbon (pretty much a lot of it not all) and it doesnt? Also just cleaned it up, w/o adjusting anything...
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Old 04-18-2011, 11:42 PM   #4
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Re: Check Engine Light/High Idle..HELP!!

I never noticed that until last night when I was doing some reading up on it. Im not sure about the IAC yet though. As far as the TPS, I just replaced it in November and adjusted it accordingly. All this stated happening shortly after I noticed the plug wires dangling down on the exhaust manifold and was causing it to arc out. Could that have fried the circuts in the sensor? I did check the codes and realized the two codes being thrown are 22 and 44. Code 22 is the TPS, code 44 is lean exhaust. Will the TPS cause a lean exhaust as well?
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Old 04-19-2011, 12:52 PM   #5
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Car: 1988 IROC-Z28 with a V6
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Re: Check Engine Light/High Idle..HELP!!

In this case, code 22 is independent of 44... You have a vacuum leak, like it or not, which is why the O2S is reading lean. Can be pretty much anywhere on a 2.8, from the valve covers on up.

There isn't really any circuit in the TPS... It's merely a potentiometer, with power on one side, ground on the other, and a sweep bar sending the voltage difference between the power and ground, along the internal resistance wire, to the ECM... Shorted out plug wires are a good way to fry your ignition module, however (been there). IIRC, code 22 is for TPS low, so I'd adjust it to where it should be and then find and fix the vacuum leak.
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Old 04-20-2011, 12:30 AM   #6
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Re: Check Engine Light/High Idle..HELP!!

So could the O2 sensor be bad and give the ECM reason to operate in open loop mode causing the codes to come up? Or could there be a vacuum line somewhere that I missed and it be the one leaking? Reason I ask is because I just replaced ALL of the vacuum lines about a month and a half ago. Im confused as to why it has such a high idle and it still running lean.
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Old 04-20-2011, 11:23 AM   #7
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Re: Check Engine Light/High Idle..HELP!!

Vacuum leaks doesn't necessarily mean it's a vacuum line it could be a plenum gasket, throttle body gasket, egr tube gasket etc you could do the starter fluid trick and spray it around the vacuum lines and anywhere that could create a leak and see if the idle jumps and if it does you found your problem. Make sure you set the TPS the way it should be too or you will never figure it out. While your messing with the TPS with the multimeter it wouldn't be a bad idea to check it to see if the voltage goes up smoothly without jumping around. I was working on a 92 cadillac hearse that was idling at 2k rpm and it was a faulty TPS and it didn't throw a code.
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Old 04-21-2011, 02:13 AM   #8
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Re: Check Engine Light/High Idle..HELP!!

So maybe it's not the TPS. If it's just a vacuum line or a bad gasket, could that throw a TPS code as well as a lean exhaust? I'll do the starter fluid test like you said, but if it's not a vacuum leak, then what could it be?
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Old 04-21-2011, 05:30 PM   #9
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Re: Check Engine Light/High Idle..HELP!!

Set the TPS to .54 VDC and see what happens first...

ANYTHING that's not sealed between the intake ports on the cylinder heads and the MAF sensor constitutes a vacuum leak. This includes:
Intake manifold gaskets
Valve cover gaskets
PCV valve, grommet, and tubing and all attachment points to the throttle body and intake manifold
Crankcase breather tube elbow at pass side valve cover and at the intake bellows connection (had my original bellows split where the tube comes into the bellows)
Fuel Injector o-rings on intake manifold end
Intake plenum, upper and lower, gaskets
Throttle body gaskets, mounting and top cover to main body
IAC motor to throttle body gasket
Vacuum line T in the back of the upper plenum
Vacuum check valve in the brake booster and connection to both the hose and the booster
Vacuum ball tank under driver's side battery tray
HVAC control head valve in the passenger's compartment
Intake air box between intake bellows and MAF sensor
MAF sensor connection at the air box
Evap canister solenoid and all inline valves
ANY vacuum hard line at the connection to whatever device (elbow on the EGR valve and/or solenoid, elbow on the fuel pressure regulator, etc)
EGR tube to plenum gasket and EGR valve (remove and clean the valve... Could be stuck open creating a vac leak).

Also may have a broken part somewhere... I had one of the mounting ears for the TB break off of the upper plenum on me (metal fatigue, same as my original alternator's front housing) and create a nice vacuum leak until I discovered it and had it fixed before I completely replaced the plenum and TB with 3.1 parts.
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Old 04-21-2011, 05:30 PM
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