156 erratically over revving on own - Alfa Romeo Forum
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156 erratically over revving on own

Hi Guys, I was wondering if anybody could shed a light on this problem? My 156 started erratically over revving on it's own at about 4000rpm. I have had a friend look at it who owns a garage, but even with diagnostic tests can find no answer!

This is what has already been done to it without resolve:

1: The MAF air flow meter has been changed from a perfectly running 156 without success

2: Idle air control changed

3: crank shaft breather changed

4: Throttle body cleaned

5: Checked for air leaks

Nothing has fixed the problem and it's beginning to drive me mad I can't really afford to buy another car ( I love my car! ) or get involed with alfa specialists.....I just need advice
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Did you clean the throttle before or after this started happening?

This can happen when you physically move the butterfly valve (metallic hinged part of the throttle body right after the MAF) as you might have done while cleaning it.

You can try resetting the ECU -you should reset it when messing around with the intake like changing an air filter etc, buuut there have been reports of owners damaging the throttle body by physically moving the valve, this thread for instance:Alfa Romeo forum: Warning for selespeed DIY owners

I'd just try an ECU reset before calling it damaged though. It only takes an hour or so -
Disconnect negative battery terminal for a good half hour, reconnect, key to MAR for 90 secs, key to STOP for 90 secs, start car without touching throttle, run for 15 mins. Or take it to your local mechanic and they can hook it up to a computer and find out straight away.

Oh and it could also be the oxygen sensor, breather tubes leaking air (you have to use special sealant in addition to the clips, a leak somewhere in the exhaust, head gasket etc etc doom gloom.

I've had this happen too, so I know it's a pain. The worst is when you're in traffic and the car is revving like a race-car on the spot, then you creep forward with a little gas and the car jerks forward and you pounce on the brake

Big headaches. Hope it's an easy fix. If the reset doesn't help, better get it looked at. It could be something stupid like a tiny leak.


Last edited by Dreska; 27-11-10 at 06:42. Reason: Added more info
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Need a little more info, what size engine, year of car, engine spec (CF2 or CF3). Might be worth invseting in a VAG cable and downloading fiatECUscan.
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Throttle re-set usually cures this problem on my 2.5 156. Good Luck.
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Did you ever find a solution to this?Im having the exact same problem.
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