over reving?
 

hi new to this i now have a 96 t5 but it has a small problem theres a delay in the revs dropping when you throttle off to change gear or slow down its only a second or so but it makes it difficult to drive smoothly and the higher your reving before you change gear the higher the revs stay i have a friend with t5 who's got the same problem i've only last week had it in the garage for a cambelt and they cleaned the throttle body for me but its made no differance can anyone help please

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RE: over reving?
 

Hi Bob,

Greetings from Narita, Japan.

Welcome to the forum, I hope you find it useful & enjoyable.

As to your problem, is the transmission mode in "SPORT"? If so, simply switch back to the "ECONOMY" mode. In Sport mode, the engine wants to reach higher RPM before shifting, and this may be causing your symptom.

If, however, your mode control switch is in ECON, is the amber arrow in the instrument cluster blinking? Also, check the condition & level of the transmission fluid (Dexron-III/Mercon). The fluid should be clear red and should not have burnt odor to it. Checking for transmission fluid is much different from checking the engine oil; you can't just pull out the dipstick. Let me know if you need an instruction as to how to check the transmission fluid level.

I hope this gets you started.


JPN

RE: over reving?
 

Bob,

I would check all the linkage under the throttle body cover. Just remove the cover and look at the throttle linkage. Have someone work the throttle while you watch the mechanism. It sounds like maybe the throttle cable or some of that linkage is binding up. I have also seen the throttle cable get "kinked" at the adjuster and cause it to return slowly.

Also, reach down in there and work the throttle by hand (with the engine off) there should be some pretty stiff spring tension.

Do the manual trans cars have a "blow off" or "pop-off" valve? If so could this be broken?

My guess is that either the linkage/cable is binding or broken return springs.

RE: over reving?
 

hi ,
thanks for your help i have a manual gear box so no sport mode i've had a look at the throttle body and butterfly all seems ok and whats a pop off valve ?

RE: over reving?
 

A pop off valve or blow off valve is installed on a turbo charged manual transmission car. It is set at a pressure above the wastegate pressure. What it does is, when you abruptly let off the accelerator and the butterfly closes there is a "surge" of boost pressure which is not so good for the turbo, hoses, throttle plate etc. It is like a "pressure relief valve" like on an air compressor. It dumps the pressure to the atmosphere or the inlet side of the turbo or the exhuast. If you watch some auto racing with turbo charged cars you will often times see them blow flames from the tailpipe under hard deceleration. This is usually because of the over rich mixture and boost being dumped into the exhaust system.

Does the throttle cable return smoothly?

All indication point towards throttle sticking. BUT, since the computer controls the boost, it is possible that it should dump boost at closed throttle and is not. This could be causing the throttle plate to be forced or held open. What does the boost gauage read at throttle off and could the Throttle Position Sensor be bad?

You have to excuse my lack of experience with Manual Transmission 850's, you see here in the States the bulk of Volvo Owners are lazy and purchase Automatics. I myself prefer Manual since my First 2 cars were from the UK (1971 MG Midget and 1974 MGB) Seems that American drivers prefer to spend more time putting on their makeup, shaving, talking on the phone, eating or drinkingthan actually SHIFT while driving.

I am still very convince the issue is with the throttle somehow. It could also very well be the nature of the Manual Turbo car.