DigitalSynthesis

Hey guys... back for another Q...

My '89 N/A has an annoying tendancy to have the RPM's "duck" a bit after I start driving from a standstill (either a deliberate launch or just normal driving... doesn't seem to matter). It seems to do it no matter whether I feather the clutch or just let it off... I don't think its my driving style since other manuals I drive don't do that. Its like the engine starts to rev up with a good amount of power -- and then it just jumps down to like 1250-1500 RPM or something and sputters up from there. Once its past about 2k it takes off pretty well, but nothing like I'd expect from it. Are there any reasons why it might behave this way?? I'm a bit concerned, now. I've checked the TPS, its seems to be good, I don't know how to check the AFM, but I've had no trouble in the higher RPMs (past ~2k). No hesitation anywhere else, just on starting to drive it off a light or whatever.

I'd really appreciate some clues here... I am new to fixing cars myself and haven't a lot of experience to go on here. Thanks!

Cosmo Donk

See if another driver has the same problem Also, what kind of clutch is in there? Some aftermarket clutches will catch pretty quickly from a standstill. What happens if you rev it to 5K or so and let it out quickly? Does it bog down like you are describing?

When does it "jump down" do 1250-1500? When you are letting out the clutch?

Rxmfn7

iTrader: (4)

Well, Id say that if it is just doing it from a hard launch, that your clutch may be slipping. But if it is doing it on normal pulling out, all the time, then it may be a TPS problem...but not too sure.

DigitalSynthesis

Yeah, it jumps when I let out the clutch... its a brand new, OEM clutch I had professionally installed (by a very reputable local shop, not by the dealer).. but the other -original- clutch behaved similarly (tho not as bad 'cause the clutch would slip so bad it didn't really start grabbing all that fast anyway).

I'm a bit afraid to rev it that high and drop the clutch... I had to pay $750 for this one and don't want to burn it out yet...

DigitalSynthesis

... brand new being around 1200 miles on it now...

Cosmo Donk

Maybe sticking throttle plates. Quite an odd problem so it is hard to figure out. When crusing will it hesitate at all iff you let off the gas completely and then step on it a little?

DigitalSynthesis

Hmm... haven't particularly noticed that, except when cruising at low speeds, then, yes, sometimes I think. It may be related to that jumping/bucking issue that remains largely unresolved with most people... hope this one has a fix!

If it *were* sticking throttle plates, how would I go about fixing/checking that?

Cosmo Donk

Hmm.. If the TPS is definitely in check than I am out of ideas right now.

To check the TB you can turn the car off and manually move it to see if it feels sticky. Just open the hood and find the throttle cable and follow it to the TB. Now slowly open and close it with your hands to see if you feel any kind of sticking. To fix it you will probably have to clean it or adjust it.