Engine rev Issue

[Marks924S]

Okay so I have an 87 924S, it has the 2.5 liter 8v engine. The car has had this problem since I've owned it, When I rev the engine above 2k it doens't stop revving for a few moments, For example When I shift from 1st to second ( I shift at about 3-3.5k and the engine RPM stay at 2k for a second or so. But when I autocross or get on the Highway if I take the RPMs about 4.5k it winds right back down properly. What may be the culprit and how to fix it? Or is this normal?

[Aufenbahn]

Sticky throttle cable?

[wild man]

Tighten up the spring maybe?

[Marks924S]

I have a weltmiester throttle cam, but I tightened the throttle cable and the throttle body butterfly returns and close properly, could it be in the air flow sensor? also when I first start the car it doesn't do this untill it warms up a little.

[IB RearWheelin]

mine started doing this when I installed the Autothority chip. i thought it was normal...

[HondaDustR]

It could be the AFM is worn. Maybe a vacuum leak? Sticky idle stabilizer? There's lots of large vacuum hoses under the intake manifold that can deteriorate and leak.

[Marks924S]

I'll give those hoses a look, and check out the AFM. If I get the time I'll try to post a video link. Thanks again.

[v2rocket_aka944]

throttle position sensor may need adjustment, when you drop throttle while shifting it cuts fuel over like 1200rpm so the engine rpms drop. it may have a faulty contact.

on a side note, why do you only rev your car to 4500? thats when the fun begins.

[Marks924S]

Originally Posted by v2rocket_aka944

throttle position sensor may need adjustment, when you drop throttle while shifting it cuts fuel over like 1200rpm so the engine rpms drop. it may have a faulty contact.

on a side note, why do you only rev your car to 4500? thats when the fun begins.

How may I go about checking the TPS? it should be on the throttle body I imagine?

And just day to day here to there I rarely take the revs above 4500, but I definitely know what you mean on the track and auto-cross it's really snappy above 4500. One other thing these cars don't have a rev limiter correct? is it safe to bring it up to ~6000-6200?

[Rasta Monsta]

Originally Posted by Marks924S

is it safe to bring it up to ~6000-6200?

For your convenience, Porsche installed a dial-type rev counter in the dash upon which maximum safe engine speed in indicated by red markings.

[Marks924S]

Could this be called a redline!?? haha

[v2rocket_aka944]

944 and 924S have a rev limiter at just over 6500RPM. when you hit that RPM the fuel cuts off until it is at a normal speed again.

there is absolutely no reason not to run the hell out of the car and shift at like 6400rpm, it likes it that way.

[John_AZ]

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[Marks924S]

Originally Posted by v2rocket_aka944

944 and 924S have a rev limiter at just over 6500RPM. when you hit that RPM the fuel cuts off until it is at a normal speed again.

there is absolutely no reason not to run the hell out of the car and shift at like 6400rpm, it likes it that way.

That's more or less what I was looking to hear. Thanks very much!

[mxfrank]

The DME is supposed to cut fuel when it senses the throttle is fully closed. Sounds like something is either broken or misadjusted. Here's a nice writeup on how it can be adjusted:

Shudder - 944 Engine

[HondaDustR]

Originally Posted by v2rocket_aka944

there is absolutely no reason not to run the hell out of the car and shift at like 6400rpm, it likes it that way.

Oh, yeah...throw in fresh rings, bearings, a valve job, a 944MAX chip, MSD Blaster 2 coil, and a 2 chamber muffler and it will like it up to more like 6800rpm. Mine will pull completely off the clock in 3rd gear easily. I don't do it all the time though because the valve springs aren't that happy up there. Need some turbo springs next head rebuild. Better cam and solid lifters would probably net useable power at 7200 pretty easily. Pretty remarkable engines for their day I'd say.


Come to think of it, your symptoms sound exactly how mine behaved when I ran with the TPS unplugged to do some WOT activation testing awhile back, so the above posts are very likely right on. Check the adjustment so that it audibly clicks when the throttle shuts and test that the switch actually closes its circuit. It's a little plastic thing with two radio shack switches that costs $80 new.