Erratic rev counter movement

[hmgabriel]

My Boxster 99 2.5 is about 140 Km. Recently the rev needle started to move up and down erratically for periods (it seems to happen when its wet weather?!) and then it normal again. The engine runs as normal. I understand the signal for rev counter comes from DME, and for DME from cramshaft sensor (is this the pulse sender?). I think it might be a display problem or poor connection, DME problem or a sensor problem. Any ideas about making a diagnosis? Thanks

[Tool Pants]

Or you might have a bad cluster. If you have a friend with a 1997-2000 you can swap clusters and see if that is the problem. Or go to the dealer and get hooked up to the tester.

[deliriousga]

Several things you can check:

1) Sticking Idle Air Control Valve. Cleaning can help if it's possible in the Boxster. I have not tried cleaning it in the Boxster, but in the 928 a little WD40 in the valve took care of the problem.

2) Dirty/bad MAF. You can remove it and clean it with some electronic parts cleaner and see if it helps before you consider replacing it.

3) Bad O2 sensor(s). They should last about 100K miles, but can go bad and cause the DME to change the mixture irradically.

Just a few things that cause that type of problem.

[hmgabriel]

"Several things you can check: 1) Sticking Idle Air Control Valve. 2) Dirty/bad MAF. 3) Bad O2 sensor(s). "

Thanks. The engine runs normally, though. If it was one of these would't you expect the engine to run erraticly as well? (what is the MAF by the way?). Thanks HMG

[ickle_monster_au]

Thanks. The engine runs normally, though. If it was one of these would't you expect the engine to run erraticly as well? (what is the MAF by the way?). Thanks HMG

I just went through this loop.. Turned out to be 2 mildly cracked coils. At your age / distance expect them to go.

PL

[alfatony]

[if your engine runs normally, it most probably is the cluster. If you buy a replacement make sure it is compatable with your year and model as the application changes and also the connectjors on the back are different for some model years.

[hmgabriel]

UPDATE

The erratic movement increased steadly and now the pointer stay at zero for periods. I had the coils and MAF replaced at scheduled maintenace.

Got a OBD cable at 50€ on ebay (ELM323 based) which worked fine with scantool and digimoto lite. On OBD the rev counter works well (so no reading problem, possibly a cluster failure). No error codes either.

Next I got a used cluster on ebay with the same color connectors (although a diferent model) but for my surprise it works well except for the rev counter (that is erratic as was the original).

Any ideas? can it be a connection problem (cables/connectors)? What to do next?

Thanks