Paging TJWONG
Thread Starter
Safety Car
Joined: May 1999
Posts: 3,651
Likes: 5
From: Atlantis
Cruise-In I Veteran
Paging TJWONG
Hey TJ,
I have a mysterious little 'issue' that is driving me bazonkers.
SD, TPI, '727' ECM, $8D code.
No EGR, No CCP, No VATS.
I have the infamous RPM Flareup at start.
Engine cranks up just fine, runs great, BLM's & INT's 128 +/- 5 across the board.
Runs really good in all modes.
Here's the 'issue':
On warm starts the engine RPM will jump up to 1400/1500 RPM and immediately settle back down to 800 RPM.
Actually it does this on cold starts but on a cold start I 'kind' of expect this.
Doesn't matter what the engine temp is. 180* and on start it jumps up to 1400 to 1500 RPM and takes about 1~2 seconds to come back to the idle speed I have in the EPROM which is 825 RPM IIRC.
I've adjusted the IAC park position down to 25. Hasn't affected it at all.
The Park/Neutal switch is working.
I've adjusted the IAC Learn Min & Max Temp down to values that the engine will experience while running.
The idle is constant/steadyno issues with 'roaming idle' speeds.
It just is driving me nuttazoid trying to control this and not finding anything that affects it or even changes the characteristics at all.
I'm wondering if there is a time lag before the MAP is sensing the run Manifold Pressure and the ECM is trying to compensate by opening the IAC up quickly during the start sequence.
Got any ideas what I can try to stop the start idle rpm flare?
I have a mysterious little 'issue' that is driving me bazonkers.
SD, TPI, '727' ECM, $8D code.
No EGR, No CCP, No VATS.
I have the infamous RPM Flareup at start.
Engine cranks up just fine, runs great, BLM's & INT's 128 +/- 5 across the board.
Runs really good in all modes.
Here's the 'issue':
On warm starts the engine RPM will jump up to 1400/1500 RPM and immediately settle back down to 800 RPM.
Actually it does this on cold starts but on a cold start I 'kind' of expect this.
Doesn't matter what the engine temp is. 180* and on start it jumps up to 1400 to 1500 RPM and takes about 1~2 seconds to come back to the idle speed I have in the EPROM which is 825 RPM IIRC.
I've adjusted the IAC park position down to 25. Hasn't affected it at all.
The Park/Neutal switch is working.
I've adjusted the IAC Learn Min & Max Temp down to values that the engine will experience while running.
The idle is constant/steadyno issues with 'roaming idle' speeds.
It just is driving me nuttazoid trying to control this and not finding anything that affects it or even changes the characteristics at all.
I'm wondering if there is a time lag before the MAP is sensing the run Manifold Pressure and the ECM is trying to compensate by opening the IAC up quickly during the start sequence.
Got any ideas what I can try to stop the start idle rpm flare?
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Try performing a minimum air rate adjustment. With the IAC totally closed set the throttle stop screw so that the engine idles at approximately 550 to 600 RPMs. Before doing this, its a good idea to clean the throttle plates and the body. Double check the TPS adjustment as well, and check the TPS for a linear output. I have seen older TPS sensors do weird things after thousands of miles of use. I had one that drove me nuts, the voltage was actually varying on its own without any throttle movement.
Le Mans Master
Joined: Jan 2000
Posts: 6,595
Likes: 1
From: Thornton CO
Originally Posted by tjwong
I had one that drove me nuts, the voltage was actually varying on its own without any throttle movement.
