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Idle problem by Tom Piantanida
Started on: 01-16-2014 01:04 PM
Replies: 13 (378 views)
Last post by: Lou and Blue on 01-20-2014 04:06 AM
Tom Piantanida
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Report this Post01-16-2014 01:04 PM Click Here to See the Profile for Tom PiantanidaClick Here to Email Tom PiantanidaSend a Private Message to Tom PiantanidaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Intermittent problem on my 1988 GT/5 speed that has become permanent. When the car is first started, it will run fine – the system is in open loop. But when the car heats up enough to go closed loop, the car won’t idle. The idle hunts between about 1500 RPM and close to stalling. This alternation between good idle and close to stalling occurs very rapidly – about two seconds per cycle. When the engine is near stall, the CHECK ENGINE LIGHT comes on briefly until the idle picks up again. If I can get the engine to run above about 2000 RPM then it runs fine, but it is sometimes very difficult to get the revs up because of the idle hunting. I checked the codes and none are set. My thought is that the speedometer buffer is not talking to the ECM. I checked the continuity between the speedometer buffer output (2000PPM square wave) and the ECM and it is good. I thought the connector on the buffer circuit board might be corroded, so I cleaned that and the contact on the circuit board. The problem persists. What else can it be??? Thanks
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phonedawgz
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Report this Post01-16-2014 03:30 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
This is not a VSS/Speedo problem.

Check fuel pressure. How old are the plugs?

[This message has been edited by phonedawgz (edited 01-16-2014).]

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Csjag
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Report this Post01-16-2014 03:45 PM Click Here to See the Profile for CsjagClick Here to Email CsjagSend a Private Message to CsjagEdit/Delete MessageReply w/QuoteDirect Link to This Post
Check the timing, my timing was advanced way too much and my idle was like yours, I also cleaned the IAC valve now the idle is pretty level. Mine is a 2.5 but I think it still applies to the V6.
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Tom Piantanida
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Report this Post01-16-2014 03:45 PM Click Here to See the Profile for Tom PiantanidaClick Here to Email Tom PiantanidaSend a Private Message to Tom PiantanidaEdit/Delete MessageReply w/QuoteDirect Link to This Post
The plugs have less than 10K miles on them. Could you please explain how the engine would run fine in open loop mode (when cold), but not in closed loop mode if the problem is fuel pressure? I can't see how that would happen.
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Tom Piantanida
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Report this Post01-16-2014 03:47 PM Click Here to See the Profile for Tom PiantanidaClick Here to Email Tom PiantanidaSend a Private Message to Tom PiantanidaEdit/Delete MessageReply w/QuoteDirect Link to This Post

Tom Piantanida

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Hard to check the timing with the idle so whacky, but I will retard the timing and see if that corrects the problem. Thanks for your suggestion.
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phonedawgz
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Report this Post01-16-2014 05:32 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Tom Piantanida:

The plugs have less than 10K miles on them. Could you please explain how the engine would run fine in open loop mode (when cold), but not in closed loop mode if the problem is fuel pressure? I can't see how that would happen.


The ECM is programmed to provide additional fuel when cold. As the engine warms the ECM is programmed to provide less. Low fuel pressure might allow the engine to run reasonable when cold, but when warmed up and when ECM is cutting back on the fueling the engine combined with low fuel pressure that could then cause the engine to run so poor that it starts to stall and then the ECM opens the IAC more and the engine revs up, only to repeat. It's only a 'maybe' and checking the fuel pressure can either identify it as the cause or eliminate it as a suspect.

Do you have a scanner? Does this problem start and stop exactly when the vehicle goes into closed loop?

Have you tried disconnecting the O2 sensor and see if the problem persists. Disconnecting the O2 sensor will keep the engine in open loop operation.

GM limited the range that the ECM can alter the fueling based on the O2 sensor. So while the O2 sensor input to the ECM can fool the ECM into leaning out the engine it shouldn't be leaning it out to the point that the engine stalls or near-stalls.

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Tom Piantanida
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Report this Post01-16-2014 06:09 PM Click Here to See the Profile for Tom PiantanidaClick Here to Email Tom PiantanidaSend a Private Message to Tom PiantanidaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for the explanation. I have a fuel-pressure gauge, so I will check the fuel pressure.
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Tom Piantanida
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Report this Post01-16-2014 06:29 PM Click Here to See the Profile for Tom PiantanidaClick Here to Email Tom PiantanidaSend a Private Message to Tom PiantanidaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Static fuel pressure (engine not running) is 44 psi. Is that high enough?
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phonedawgz
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Report this Post01-16-2014 07:26 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
The target is 42 - intake manifold vacuum so yeah that is well within range.

No OBD1 scanner I take it?

[This message has been edited by phonedawgz (edited 01-16-2014).]

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Tom Piantanida
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Report this Post01-16-2014 09:26 PM Click Here to See the Profile for Tom PiantanidaClick Here to Email Tom PiantanidaSend a Private Message to Tom PiantanidaEdit/Delete MessageReply w/QuoteDirect Link to This Post
No, no scanner. What would that tell me if I had one? Thanks.
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Lou and Blue
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Report this Post01-16-2014 09:38 PM Click Here to See the Profile for Lou and BlueClick Here to Email Lou and BlueSend a Private Message to Lou and BlueEdit/Delete MessageReply w/QuoteDirect Link to This Post
Maybe try this? My car has anup and own idle once its warmed up but if its running in the driveway it'll get hot and not hunt for idle.
I'm gonna investigate this this weekend on my car.

http://www.fiero.nl/forum/Forum2/HTML/043240.html

Worth a shot!

------------------
Louis Duet
Baldwin, Long Island, NY
"Blue" <= '85 GT
"Gettin' There"

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phonedawgz
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Report this Post01-17-2014 09:28 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
It would tell you if the ECM is seeing the right temperatures for the CTS and IAT. Maybe they are causing the trouble, maybe not.

MAP could be way off, but that doesn't seem to be so likely since this is temp related.

I sell an aldl scanner cable that works with your Windows laptop - http://reddevilriver.com/aldl.html - $55.00 shipped
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Csjag
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Report this Post01-18-2014 08:24 AM Click Here to See the Profile for CsjagClick Here to Email CsjagSend a Private Message to CsjagEdit/Delete MessageReply w/QuoteDirect Link to This Post
Did you ever try checking the timing?
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Lou and Blue
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Report this Post01-20-2014 04:06 AM Click Here to See the Profile for Lou and BlueClick Here to Email Lou and BlueSend a Private Message to Lou and BlueEdit/Delete MessageReply w/QuoteDirect Link to This Post
I think it's due to a dirty IAC. I'm going to remove,clean, and reinstall mine to see if it helps. I ave the same issues you do. If I let it warm in the driveway it idles just fine, but after coming off the highway, it's up and down dipping oil pressure into the red zone and back and forth.

Have you tried cleaning the IAC and IAC port already?

------------------
Louis Duet
Baldwin, Long Island, NY
"Blue" <= '85 Fiero GT
Stock V6---Stock everything.
~~~~~~~~~~~~~~~~~~~~~
"Boo" <= '81 Delorean DMC-12
VIN #5835
Stock PRV engine
Robertson Equipped
Neiland/Delman Engineered
Carbed and loving it! (Peugot 604 manifold) ---"Sorry purists"

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