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86 ISC weird behavior


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#1 arbor

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Posted 19 March 2020 - 06:09 PM

So full disclosure I do not have the MAF on the car, I bought it this way and it runs really well without it. no other weird issues to report.

The only thing I can not seem to figure out is this weird cold start issue where the car will start and idle up to around 1k+ rpm and just stay there, it will never idle back down to were the ISC/tps was set at 850 give or take.
I have had the ISC apart cleaned the gunky old grease and cleaned the motor brushed and verified it works. The ISC checks out when following the service manual  tests.

I have reset the ISC multiple time and it always behaves the same way, cold start with just sit at 1k+ and stay there. the only way I can get it to idle back down to 850 ish is to turn the car off then turn the ignition on for 15 sec (let the ISC move) then start the car and then its normal for the entire time i'm driving the car.  

Has a new CTS install which ohms out correctly against the service manual at least at cold temps.
Throttle cable doesn't seem to be hanging the linkage up, so I am wondering if this is just the nature of the car with out the MAF.

Any one with an 86 chime in on this?





#2 tux

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Posted 23 March 2020 - 09:57 AM

Without MAF I would have to hold the gas to maintain idle.

I ended up tossing a 1g MAF in and its back to fine.

#3 arbor

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Posted 26 March 2020 - 04:19 PM

View Posttux, on 23 March 2020 - 09:57 AM, said:

Without MAF I would have to hold the gas to maintain idle.

I ended up tossing a 1g MAF in and its back to fine.

Is yours an 86? The 86 are very different in terms of the ECU setup compared to the later cars.

#4 tux

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Posted 26 March 2020 - 07:29 PM

View Postarbor, on 26 March 2020 - 04:19 PM, said:



Is yours an 86? The 86 are very different in terms of the ECU setup compared to the later cars.

Yep my 86.

#5 arbor

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Posted 07 April 2020 - 03:10 PM

Well I went through 3 boxes I got with the car which came with 3 maf's, plugged the maf back in and now the car will behave how it should, so I will be installing permanently now.

So it seems yes the car will run just fine with out the maf but requires some do hickery to get the car to idle correctly without it, it is also pig rich without the maf at idle.

#6 Tim_C.

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Posted 16 April 2020 - 08:43 PM

Good info.
My friend has an '87 that I used to own. It was hunting up and down. Checked a lot of things and then I decided to unplug the ISC while it was running. Idle went to normal. Plugged it back in and it stayed there. Runs great now. This was 2 weeks ago.
'87TSi .510Roller Cam, JE Forged, TS Rings & plateau honed walls, lightened rods, race prepped crank, mains line honed, balanced, 17C, 3"EX, 2"HardPipes, AlFly, rrfpr, 88trans, 3.90's w/posi plate mods, polyBushings, STSprings, KYBStruts, Camber Plates, CustomAlternator
Traded for new set of tires for my wife's Buick: '87 TSI Gold that needs just about all steering and suspension parts replaced, injectors, a new transmission, clutch, and various electrical gremlins. New owner is a mechanic who is already driving it. I couldn't stand letting it sit any more!
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