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Matt
Matt, Mechanical Engineer
Category: Toyota
Satisfied Customers: 20611
Experience:  BEng, Repaired my own cars and others for 20 years, worked in Formula 1 for 10 years
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I have a 1992 camry v6 3 liter it starts right up and revs

Customer Question

I have a 1992 camry v6 3 liter it starts right up and revs up very good in park but when I put it in drive and give it the gas it revs up and down big time. what would cause this problem ?
Submitted: 11 months ago.
Category: Toyota
Expert:  Matt replied 11 months ago.

hello

I'd suggest doing a compression test across all cylinders to check that there's no valve damage as all cylinders should be within 10-15 psi of each other

if this is OK then this could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth cleaning out the idle speed control motor / valve as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile

Customer: replied 11 months ago.
the compression is 160 on all cylinders. The new thing I have found out is it starts great idles good. Put it in reverse and it backs up smooth with power . Put it in drive and its hesitates and jerks. If I start out slow I can drive it.
Expert:  Matt replied 11 months ago.

hello

Ok I'd still check for an airleak and check the fuel pressure as the next step

if you feel the engine is not the problem then I'd next check the oil level in the transmission is up to the mark on the dipstick when its warm

Customer: replied 11 months ago.
I do not feel that it is a transmission problem in its self, its like it sends a signal to the engine to change something, but only in forward. When you go from park to reverse it actually feels smoother. When backing up I can step on the gas and it will go at any thrust without hesitation. As soon as I put it in drive the engine changes the way it runs. When driving if I step on the gas below 20 mph it will balk, above that it will take off like its off to the races for as fast as you want to go.
Expert:  Matt replied 11 months ago.

Hello

Ok this really does sound like an airleak to me as they have the most effect at low throttle openings and at idle as they make up a higher proportion of the airflow at these loads, once you open the throttle a bit then amount of air involved in the leak stays the same and so is a much smaller part of the overall

so in summary check for airleaks as the next step

Expert:  Matt replied 11 months ago.

Hi

do you still need help?

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