90 Cabbie revs to 3000rpm on start up!

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Posts: 3
Joined: Sat Mar 18, 2017 2:22 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

90 Cabbie revs to 3000rpm on start up!

Post by Daden » Mon Mar 20, 2017 11:34 pm

hey folks. My 90 cabbie, 5 speed, when you start it up it revs to 3000rpm and stays there until you unplug the iac valave. It runs fine without it but it makes for hard starting on chilly mornings. It is a digi2 car. Checked all vacuum lines and throttle screw ring, all are fine. Cleaned the iac to no differance. replaced iac with known good one, same thing. Could it be the digi control unit?

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Posts: 4073
Joined: Mon Mar 21, 2005 5:45 am
What year is your cabby?: 1992
Do you own a Cabriolet?: No
Location: Duluth, Ga

Re: 90 Cabbie revs to 3000rpm on start up!

Post by Briano1234 » Tue Mar 21, 2017 10:01 am

IAC? ISV.... silver thing in the front of the throttlebody behind the valve cover?

Automatic, or manual.....

Lets do a little checking first.
Make sure that your a/c is off (blower to 0) slides to the black area.

When you turn the car on does the ISV vibrate. (disconnecting and reconnecting the ISV with power on can blow it, or the ECU up.)

1. Have you replace the Battery to Frame and frame to engine grounds?
yes/no. No Try this. Take a battery jumper cable set, connect one to the battery negative post, and the other end to the FRAME. Take the Other lead and connect it to the Battery negative post and then attach the free end to the Engine.

1a. Is there a ground wire between the rear valve cover post, and the Coil Bracket? (same post the o2 sensor is hooked on.

Start the car. better worse? Better, get new ground wires, same or worse... next step.

2. Disconnect the Blue CTS sensor... Start the car better or worse.. Better buy a new Blue CTS sensor (don't forget the o-ring).
same worse.. reconnect it and proceed.

3. Disconnect the o2 sensor, better worse, better new o2. worse or same.

4. Check your Fuel pressure and bleed off for the FPR as outlined in the Bentley...

5. If all this isn't fixing it, then I would suspect the digifant control unit. It could also be a flakey A/C relay.... but that is doubtful.... I have only seen the a/c relay fail to boost rpm at a/c on.

I am leaning towards the FPR, I suppose it could be a bind in the throttle control linkage, so you may want to spray it with pb-blaster a few times, and check your WOT switch on top of the throttle body. With an ohm meter it should click open and closed..... I wouldn't suspect that but you never know.

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
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Posts: 3
Joined: Sat Mar 18, 2017 2:22 pm
What year is your cabby?: 1990
Do you own a Cabriolet?: Yes

Re: 90 Cabbie revs to 3000rpm on start up!

Post by Daden » Tue Mar 21, 2017 8:54 pm

Thanks Briano.
iac/isv, yes that thing!
manual, no a/c ( silly excess weight on a convertible, 8^) )
no it does not vibrate.
1. All new grounds.
1a. See 1.
2. Did that. Put new one in anyway!
3. Have not tried that! Will have a look at that when i get it out of storage the first of may.
4. wish i had a bentley. only have a haynes manual. Will check this also.
5. We'll see!
no binding in the linkage, the switches work, checked them out with the meter,
its been doing this since late summer of 2015 after it sat for two months in the driveway as i had work commitments that kept me from it. then went to start it and it did this right away. been driving it with the isv unplugged, doesn't seem to bother it to much except cooler mornings, but would like to resolve the issue.
Again, Thanks!!

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