inverted idle
Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
Likes: 0
inverted idle
I believe I have a real puzzler. My 86 tpi has an inverted Idle. when cold the idle is very low, like 500rpm, BUT when warmed up the Idle is a little high, like 1100rpm. The idle is smooth and deliberate, its just backwards. only other clue is the throttle response is a little slow.
It starts quickly, runs really smooth it just backwards. any ides?
It starts quickly, runs really smooth it just backwards. any ides?
Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
Likes: 0
no codes, TPS replaced, IAC replaced, MAF replaced, coolant sensor replaced, egr replaced, power relays replaced, ALL set up procedures done properly. I have basically done everything . The only thing I have not done yet is to have a scanner put on the car.
I have tried all the regular stuff, new vacuum lines, new intake gaskets, cleaned throttle body,
Its almost like the coolant sensor, which sends temp readings to the ECM, is backwards,
mike
I have tried all the regular stuff, new vacuum lines, new intake gaskets, cleaned throttle body,
Its almost like the coolant sensor, which sends temp readings to the ECM, is backwards,
mike
Drifting
Joined: Nov 2015
Posts: 1,709
Likes: 330
Finalist 2020 C4 of the Year - Unmodified
Is your idle screw on the throttle still sealed? If it has been opened, needs a lock nut on it, otherwise it moves.
Agree, walk through TPS adjustment and timing. IAC can be reset easily, has it been replaced recently?
Agree, walk through TPS adjustment and timing. IAC can be reset easily, has it been replaced recently?
Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
Likes: 0
No its been removed, and I have been through the IAC setup many times. the procedure to do the IAC set up all goes as it should, but the inverted idle still remains. Whats weird is that the idle itself is perfect, (except the speed) Its smooth, regular and purrs, just not at the right speed, ya know.
How is it idling so beautifully but still be backwards? Low idle when its cold and High idle when its hot?
How is it idling so beautifully but still be backwards? Low idle when its cold and High idle when its hot?
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
You need a scanner to monitor data. Make sure vacuum hoses are route correctly and all intake bolts are tight. Sometimes vacuum leak can be present when cold and go away when manifold expands as is warms up.
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Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
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The car sat outside for years. I replaced relays, switches, rebuilt the top end, ultrasound clean injectors, throttle body, I got it running really good. Quick starts, great idle, good throttle response.
I then painted it. After all the sanding painting, and buffing, I started the car and it ran like ****.
I then replaced the MAF, and ALL the sensors.
I then painted it. After all the sanding painting, and buffing, I started the car and it ran like ****.
I then replaced the MAF, and ALL the sensors.
Thread Starter
7th Gear
Joined: Jun 2019
Posts: 7
Likes: 0
It even got a new ECM.
When the radiator fan comes on, the car idles up a little like it should, the fuel pressures are perfect, it really does run pretty good, except for the inverted idle.
When I cold start the car it , starts pretty quick, and instantly goes to 500rpms, stays smoothly there until the engine is warm, and then it slowly creeps up to around 1100rpm.
If I crack on the throttle while it's at high idle, IT WILL IDLE down to a good idle speed, BUT it quickly creeps back up to 1100rpms
Thanks for the help
When the radiator fan comes on, the car idles up a little like it should, the fuel pressures are perfect, it really does run pretty good, except for the inverted idle.
When I cold start the car it , starts pretty quick, and instantly goes to 500rpms, stays smoothly there until the engine is warm, and then it slowly creeps up to around 1100rpm.
If I crack on the throttle while it's at high idle, IT WILL IDLE down to a good idle speed, BUT it quickly creeps back up to 1100rpms
Thanks for the help
Team Owner
Joined: Jul 2004
Posts: 28,430
Likes: 3,282
From: Hartford WI
Can you pause for a minute, buy a scanner and see what is going on or would you like to continue "The Shotgun Approach". When you have replaced everything from front to back, you will, by then have found the problem.
Drifting
Joined: Nov 2015
Posts: 1,709
Likes: 330
Finalist 2020 C4 of the Year - Unmodified
Setup the engine for setting timing, instructions on the radiator sticker. Should include disconnecting the EST.
Try it then. If idle stays constant, as I expect, then it's the ECM causing the change, chase from there.
You mentioned a "new ECM", what was actually replaced? The MEMCAL? The whole unit?
Try it then. If idle stays constant, as I expect, then it's the ECM causing the change, chase from there.
You mentioned a "new ECM", what was actually replaced? The MEMCAL? The whole unit?