Racing up and down at idle

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No Quarter
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Racing up and down at idle

Postby No Quarter » Mon Jul 22, 2013 3:10 am

Why does my Beretta 3.1 do that? It's happened 4 times now that when hot, idling in Drive at a red light, the engine starts to go from 500 rpm to 1500 rpm, up and down. It means that it almost dies when lowest, and I have to be hard on the brakes when highest, or it would move forward.

I've changed the TPS, it's happened both before and after that change. I think the normal idle is quite high, but I'm not sure.

Any suggestions? Thanks


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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themixer
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Re: Racing up and down at idle

Postby themixer » Mon Jul 22, 2013 7:48 am

check for vacuum leaks, and clean your TB and IAC with a good quality cleaner. Preform a proper idle relearn.



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Re: Racing up and down at idle

Postby Barry » Mon Jul 22, 2013 6:03 pm

Had a similar issue in my lumina 3.1. Turned out to be the o2 sensor... Car ran great until motor warmed up and went into closed loop. Then idle would wonder really hard. I replaced IAC but it didn't help.



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Rettax3
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Re: Racing up and down at idle

Postby Rettax3 » Thu Jul 25, 2013 5:56 pm

Usually a bad or dirty IAC valve. You could try cleaning it, but they are cheap enough that replacing it might be more worth-while. Other possible problems are (as mentioned) a vacuum-leak, (also as mentioned) needing an idle re-learn (although that usually doesn't cause that much RPM drift), maybe a bad ECM ground or a bad MAP sensor (these are less likely, without other symptoms), or even a transmission problem (try putting the car in neutral when it does this to see if it stabilizes). A sticking injector or a failing coil could cause your symptom too, but again, less likely without other symptoms. Barry's O2 sensor issue is news to me, but obviously that could be a problem too since he experienced it. Good luck.


1989 Super Charged 3800 Series II (First)Six-Speed Conversion GTU
1990 Turbo 3.4 Five-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 Five-Speed Indy GTi (Rebuild Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 3400 Top-End Auto OD Z-26

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Re: Racing up and down at idle

Postby No Quarter » Sat Jul 27, 2013 4:44 pm

" a proper idle relearn.", can that be donw w/o scan tool?


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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Rettax3
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Re: Racing up and down at idle

Postby Rettax3 » Sat Jul 27, 2013 5:06 pm

Yes. Here is how:
1. Remove battery power for one (1) minute. Restore battery power and place air conditioning controls (if equipped) in the "off" position.
2. Firmly apply the parking brake and block the drive wheels. Start the engine, shift the transmission to drive for automatics and neutral for manuals.
3. Allow the engine to run until the engine cooling fan has cycled once, or a maximum of 10 minutes.
4. Turn the ignition key to the "off" position for at least 5 seconds.
5. Repeat Step 2.
6. Allow the engine to run for at least five (5) minutes.
The correct IACV values for proper idle control will now be stored.


1989 Super Charged 3800 Series II (First)Six-Speed Conversion GTU
1990 Turbo 3.4 Five-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 Five-Speed Indy GTi (Rebuild Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 3400 Top-End Auto OD Z-26

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Re: Racing up and down at idle

Postby No Quarter » Thu Aug 01, 2013 5:58 am

Update:Found no vacuum leaks. Ran the idle reset as suggested. No change. It's also when engine is rather cold, in fact I'd saty it's at totally random times. In Drive or in Neutral. Both with and without A/C on.

I've ordered an IAC and O2 sensor, takes a while to get here. Then we'll see.


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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Re: Racing up and down at idle

Postby No Quarter » Thu Aug 15, 2013 4:59 am

Indeed the IAC, and an idle reset, as Rettax3 said.

Idle is also lower now, don't have to push the brake so hard. And it drives better. So great. Only thing is that the idle is in fact just a little lower than I want, slightly as if it's missing occasionally, again a lot better than before, but can it be raised slightly, or is the computer in control?


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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Re: Racing up and down at idle

Postby 3X00-Modified » Thu Aug 15, 2013 7:41 am

Idle is all computer controlled, it's run from the IAC... you should never adjust the throttle stop on the TB.



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Re: Racing up and down at idle

Postby No Quarter » Thu Aug 15, 2013 8:01 am

OK. Thanks Mr. Pink


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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Re: Racing up and down at idle

Postby DOHC_tuner » Fri Aug 16, 2013 10:25 am

I do not have much experience with V6 motors. But i had a similiar issue with a LD9 2.4L. Turned out to be the hose that connects to the MAP sensor. It was old and rotted out. I always over looked it, didnt think much of it. I changed out the fuel filter....helped a bit but the problem was back. Then came the decision to do the fuel pump. I did a little research and spent 2 dollars at autzone for some new hose. Swapped out the old torn hose and bam....car runs great!

Might not be your issue but its worth a shot.



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Re: Racing up and down at idle

Postby No Quarter » Sun Aug 18, 2013 11:50 am

Don't you hate it when you think you've solved and fixed something, tell the world, and then it's still broken?

After the IAC change and idle reset, it ran fin with a low idle for more than 24 hours. And then it began to have a higher idle and raced up and down once. Damn. Home and look for leaks. The PCV was not rattling well, a new has been ordered, and the old one welded shut and put back in. While doing all this and testing and starting and pulling various vacuum lines and putting them back on, the idle ended up above 2000 rpm. And stayed there. In the end I reset the idle again, and now it's nice and low. But for how long?

What's going on?


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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Re: Racing up and down at idle

Postby woody90gtz » Sun Aug 18, 2013 12:57 pm

That is weird. Mine did this with a brand new Bosch o2. Saw it was reading weird in the datalog and replaced it with a Denso o2. No problems since.

Can you hook the car up and log it? That's a good way to see what is acting funny. Eliminates a lot of guesswork. Some things can be weird without throwing a code, but you can see once you look closely.


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Re: Racing up and down at idle

Postby No Quarter » Sun Aug 18, 2013 1:27 pm

I have no tool to read any data...


1990 Beretta GT, 3.1 V6, only 45k miles, 1 owner before me
Daily driver here in Denmark, don't see many Berettas on the road here...

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Rettax3
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Re: Racing up and down at idle

Postby Rettax3 » Sun Aug 18, 2013 4:47 pm

I really hate pointing to the computer, as they are rarely the cause. It is almost sounding like you could have a bad wire or corrosion on one of the connectors for the IAC valve though. Try pulling the connectors on your computer and looking for corrosion on one of the IAC wire pins. There are four of them, two green, two blue, each pair of green and blue wires will have one wire with a black stripe and one wire with a white stripe. Also check to make sure the throttle-cable isn't kinked or binding, and if you have cruise-control, then make sure the cable from that isn't stuck either.


1989 Super Charged 3800 Series II (First)Six-Speed Conversion GTU
1990 Turbo 3.4 Five-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 Five-Speed Indy GTi (Rebuild Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 3400 Top-End Auto OD Z-26


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