Resolved 1g High Idle, no idea what it could be

[SeriozHenka]

I have a 1990 Eagle Talon TSi AWD completely stock. All of a sudden this afternoon when I went to come home from work it started to idle at 1500 rpms. This is when I'm driving it or just parked. When I got to start it it idles normally at 800 and then begins to creep up to 1500 rpms. It did this when I first bought it but then eventually went away. I never had this problem in between now and then. I usually idle at 800 rpms. Another thing to mention when its at 1500 rpms it sounds like it climbs up to maybe 1550 or 1600 and then drops back to 1500 which makes it sound like a misfire rapidly, its not rythmic as it happens are random times, kind of like a whrrrrRR Rrrr, whrrrrRRR RRrrr. I don't know if that's a good description. The car drives perfectly fine no issues at all other than that it idles at 1500 even when coasting in neutral and makes that sound. Thanks guys.

 

[o0GuitarKid0o]

Idle Position Switch and throttle cable are the most common causes, ISC as well. Lots of posts you can look into for more detail.

Also their is a procedure to set your BISS screw via grounding a pin on the obd1 port and a connector near the battery.

Also look for vacuum leaks

Your sound description sounds like idle surge, usually caused by a bad ISC.

 

[dwb]

Most likely you have a post-throttle plate vacuum leak. If I had to guess, you lost the BISS screw or a vacuum line came loose.

 

[SeriozHenka]

Idle Position Switch and throttle cable are the most common causes, ISC as well. Lots of posts you can look into for more detail.

Also their is a procedure to set your BISS screw via grounding a pin on the obd1 port and a connector near the battery.

Also look for vacuum leaks

Your sound description sounds like idle surge, usually caused by a bad ISC.

I adjusted my BISS screw to where the car now starts at about 600 rpms and climbs to 1000, this i can deal with until i find a fix, will this affect my car in the long run like hurt it? I didn't adjust it with a computer, just at temp with a screwdriver

 

[941gladiator]

I have a 1990 Eagle Talon TSi AWD completely stock. All of a sudden this afternoon when I went to come home from work it started to idle at 1500 rpms. This is when I'm driving it or just parked. When I got to start it it idles normally at 800 and then begins to creep up to 1500 rpms. It did this when I first bought it but then eventually went away. I never had this problem in between now and then. I usually idle at 800 rpms. Another thing to mention when its at 1500 rpms it sounds like it climbs up to maybe 1550 or 1600 and then drops back to 1500 which makes it sound like a misfire rapidly, its not rythmic as it happens are random times, kind of like a whrrrrRR Rrrr, whrrrrRRR RRrrr. I don't know if that's a good description. The car drives perfectly fine no issues at all other than that it idles at 1500 even when coasting in neutral and makes that sound. Thanks guys.

Did you ever find the problem to your high idle? I have the exact same issue in my 1990 Plymouth Laser. I have read your thread and didn’t see any final conclusion except you made an adjustment to the biss screw. Just checking to see if you found anything that maybe helpful as I am really new to working on cars. Thanks.

 

[SeriozHenka]

Did you ever find the problem to your high idle?

It was the IAC. I ran some troubleshooting and figured out that that was the cause. I tore apart the entire intake and throttle body, cleaned the IAC and that fixed it for about 3 days. Just an old part is all. The problem is the IAC they used for the first year, I think? So the 90 IAC is completely different and incompatible with the IAC they used for 91 and up.

The only place I was able to find a new one was eBay and it was used out of a car with 150k and he wanted 120 bucks for it. So I just live with the issue, it doesn't stall so who really cares.

 

[941gladiator]

Thanks for letting me know what your fix was. I will look at mine.

 

[arodgst]

I glad you solved yoyr problem. Ill leave this here for a good read and info for anyone who comes aross this issue and looking for some understanding as I did.

https://www.sixsigmatuning.com/dsm-idle-control

 

[We're on Boost]

The problem is the IAC they used for the first year, I think? So the 90 IAC is completely different and incompatible with the IAC they used for 91 and up.

Serioz and @941gladiator
I made a thread in 2017 that explains how to use a 1991 or newer ISC in the 1990 cars. So if your 1990 ISC kicks the bucket, you can do this.

The thread looks complicated because I was figuring it out with the help of a couple other guys in here. But the actual solution isn't that bad. All you do is swap 2 wires around in the harness, and you make all 6 of the wires longer. The electrical plug there has 6 wires to it, you swap #4 and #6 with each other. And you make all 6 of them longer. That's it.

The plug itself is the same. And the way the ISC fits in the throttle body is the same. It all works perfect when you get it put together.

The reason you have to make the 6 harness wires longer is because the 1990 ISC has wires coming out of it that are maybe 6 or 7 inches long. The 1991+ ISC doesn't. So the harness on the car has to be long enough to reach the ISC.

There are 2 brands of new 1991+ type ISCs that seem good - Standard Motor Products and WVE (used to be Airtex). They only cost about $60. I've got links to where they are listed in Rock Auto in that thread. I also made a video of it all done which is linked in that thread, and the Description field in the video explains some things too.

Here's the thread: https://www.dsmtuners.com/threads/1990-isc-motor-–-reverse-polarity-for-new-part.514056/

One thing I didn't put in that thread that I should of is a diagram of the plug showing wire numbers and colors and positions. So here is that. Wires 4 and 6 are the white one and the black one:

You must be logged in to view this image or video.

 

[941gladiator]

I glad you solved yoyr problem. Ill leave this here for a good read and info for anyone who comes aross this issue and looking for some understanding as I did.

https://www.sixsigmatuning.com/dsm-idle-control

That is the best articulated explanation I have read anywhere. I am a new comer to the DSM world and and have almost no clue how to approach repairs. This was fantastic, thank you so much for the post. You are my hero. Keeping 1G 1.8ers alive one at a time.

 

[arodgst]

That is the best articulated explanation I have read anywhere. I am a new comer to the DSM world and and have almost no clue how to approach repairs. This was fantastic, thank you so much for the post. You are my hero. Keeping 1G 1.8ers alive one at a time.

Your very welcome, I hope it all works out for you!!!! Goodluck!!

 

[pauleyman]

Did you ever find the problem to your high idle? I have the exact same issue in my 1990 Plymouth Laser. I have read your thread and didn’t see any final conclusion except you made an adjustment to the biss screw. Just checking to see if you found anything that maybe helpful as I am really new to working on cars. Thanks

That is the best articulated explanation I have read anywhere. I am a new comer to the DSM world and and have almost no clue how to approach repairs. This was fantastic, thank you so much for the post. You are my hero. Keeping 1G 1.8ers alive one at a time.

It should be. Very prominent long time dsmer Kevin Jewer wrote it.