Hi all,

These are the issues of a Maserati 1990 (Quattroporte) 422, 2000 SL.6 cylinders, fule injection.The car lives in Greece, and is in pristine condition.

1) The rpms go up when the engine is idle (no gear?) e.g when you stop at a light. Apparently this is an unexpected behavior. Could you give me a list of possible reasons?

2)When we start the car and/or go from 1st to 2nd gear, the engine doesn’t “fire” right away. There is a lag, as if the car stops.



You say 6 cylinder, I’m not aware of Quattroportes ever having a 6 cylinder. Is it instead a Biturbo?

OK, it’s a 4-door Biturbo, model 422 (says Wikipedia). As for your problems, 1) sounds like an engine control/computer/sensor problem, 2) may be related to 1), or could be an injector problem.

Unfortunately, these are difficult cars to get to run correctly. Finding a good mechanic is usually required.

Thank you for your reply. My mistake/ignorance: it is a Bitubo model. The MAserati club here in the States suggested it could be a bad throttle position sensor. We’ll look into that.
Another question: They replaced both turbos, but used a little bigger ones cause they couldn’t find the exact same size; they can handle up to 2 Atm. do you think this is a problem? The car runs fine (except the issues on my first post).


Hmm, I have not worked on a Maserati before, but there are some universal things that can apply here so I’ll offer some info and advice.

When it comes to turbos the main issue you will see when you move up in size is an increase in turbo lag, or in other words that delay between depressing the gas and getting an actual response. Most turbo cars exhibit it to some degree, and the older the car the more obvious. People will suffer through this though to enjoy the benefits of increased turbo size which include more air flow and lower temperatures. Personally I prefer smaller turbos and snappy response. A slightly larger turbo should not affect idle speed however.

As for idle speed going up in the vehicle there are a few possible reasons, but it usually doesn’t involve the computer itself being defective. Somehow you’re seeing additional and uncalled for air making its way into the intake manifold. If this vehicle has an idle air control valve it may be dirty or defective. You may also have a vaccuum hose that is leaking allowing excess air into the intake as well. Investigate these two areas and see what turns up.

This vehicle is quite old at this point and the operating system is primitive, so a quality european car shop should be able to quickly sort this out.

The larger turbos shouldn’t be a problem (other than slightly delayed throttle response, a Dave G. mentions) if the the maximum boost is unchanged. Good luck, the Biturbos are unfortunately well known for being very difficult to keep running smoothly.