98 Camry: Poor acceleration

[tpeter]

I have a 98 Camry with 5s-fe. I have had the cambelt, spark plugs, oil replaced in October about 5000km before (except the oil, everything is from Toyota, the plugs have been really bad condition before). After the whole thing I have felt the engine being a little stronger, but that vanished after a week or so. Since then it is really slowly accelerating.

Do you have any idea?

Some more info:
- I can race the engine to 5000 rpm without a problem (of course slowly), thus I believe it has nothing to do with gas filter or pump.
- I have some bad engine mounts, but the clutch is in a good state, it is not slipping, so I don't believe it has to do with that.
- I have just replaced the air filter yesterday, but I don't feel much of a difference. I think that the air filter has become a little dirty, but that's more like a feeling, as the air is quite clean where I live, thus even Toyota doesn't replace it every 10000k, just clean it with compressed air.
- In December the mechanic verified the ignition system and there were no fault codes at that time.
- I don't see any smoke coming out of the exhaust.
- It is a little noisy when it is cold.
- It has some sound when accelerating on a hill with low rpm. It is only audible when the windows are down.

[fenixus]

check a few things like Throttle Position Sensor, Engine Coolant Temperature sensor and the Idle Air Control valve (under throttle body).

also make sure the emissions systems are working fine as they CAN mess up car's performance when working badly. I mean here EGR (unholy trio of EGR valve, modulator and VSV - electrically operated vacuum switch valve, and all vacuum hosing interconnecting them), EVAP (check simple things like try new OEM gas cap, check VSV and vacuum hose to it coming from throttle body) and PCV (1 valve on top of valve cover and hose to intake manifold and another hose at opposite edge of valve cover to intake hose) - any vacuum leak or blockage in any of those subsystems will throw the ECU controlled system off, not always throwing trouble codes.

[nathanours]

You could try a fuel system cleaner maybe? I added a can of BG44K to my car and it made it run a lot smoother. Also, when mine was a little sluggish I cleaned out the throttle body with sea foam, and that made it more responsive.

[mgartner0622]

Can you do a 0-60 or 0-40 and let me know your time?

That way we can judge just how slow it is. My camry didn't have anything done to it besides oil changes for 130k and originally did it in 19 seconds (0-60) but after changing the transmission fluid, using Sea-Foam and changing the spark plugs I got it down to 15.5.

[fenixus]

what do you use for measuring it precisely and where (level ground not easy to find around here)?

Originally Posted by mgartner0622

Can you do a 0-60 or 0-40 and let me know your time?

That way we can judge just how slow it is. My camry didn't have anything done to it besides oil changes for 130k and originally did it in 19 seconds (0-60) but after changing the transmission fluid, using Sea-Foam and changing the spark plugs I got it down to 15.5.

[tpeter]

Originally Posted by fenixus

what do you use for measuring it precisely and where (level ground not easy to find around here)?

I will try to measure it exactly. It is also hard to find flat surface here in Auckland. Also on the weekend I will try to examine the suggested things.

Although I couldn't measure it accurately I have tried to accelerate some. I would update the statement, slow acceleration below 2000 rpm. It is the most obvious in second gear, where it should be responsive. May be I have not mentioned before I have a manual.

[fenixus]

slow acceleration below 2k rpm could be an IAC valve dirty and unable to close/open when needed.
other than that I would check resistance of the Throttle Position Sensor throughout full range of throttle, it should be growing in a linear fashion, yours could be fluttering or showing resistance drop at some spots instead of increase.

I have some app (Torque Pro) on my android which features something like 0-60mph, but have never used it yet and have no idea if it works accurately (if at all). but then you would need to use it too in order to compare results, otherwise makes not much sense.

[tpeter]

Do you check the throttle position sensor with disconnecting the wire and measuring resistance on the leads, while pulling the throttle?

On a hill when I'm below 2k rpm and I push full throttle the engine sound changes, it goes deeper. So I guess ultimately the sensor is correct, as something happened.

What do you use for cleaning the IAC valve?

Also what is the mechanism why IAC valve causes trouble? If it closes then the motor gets too much air, whereas the if it doesn't air is not enough?

Originally Posted by fenixus

slow acceleration below 2k rpm could be an IAC valve dirty and unable to close/open when needed.
other than that I would check resistance of the Throttle Position Sensor throughout full range of throttle, it should be growing in a linear fashion, yours could be fluttering or showing resistance drop at some spots instead of increase.

I have some app (Torque Pro) on my android which features something like 0-60mph, but have never used it yet and have no idea if it works accurately (if at all). but then you would need to use it too in order to compare results, otherwise makes not much sense.

[fenixus]

yes, I check it with connector unplugged, leads touching sensor's terminals VTA and E2 while I move the throttle manually "by wheel".

you can try any oxygen sensor safe Throttle Body cleaner to "clean" the IAC by spraying some of the stuff into from TB. it won't help much anyways, but you can try.

ECU manipulates the IAC shutter to get more or less air (or none). over years the air pollutants and oils from PCV system will make it dirty and carbonized making the shutter sticky and moving in limited range (usually unable to fully open and unable to fully close).
sometimes the tiny electrical motor of IAC can go bad too on top of that.

it rarely throws any codes unless it's simply unplugged.

Originally Posted by tpeter

Do you check the throttle position sensor with disconnecting the wire and measuring resistance on the leads, while pulling the throttle?

On a hill when I'm below 2k rpm and I push full throttle the engine sound changes, it goes deeper. So I guess ultimately the sensor is correct, as something happened.

What do you use for cleaning the IAC valve?

Also what is the mechanism why IAC valve causes trouble? If it closes then the motor gets too much air, whereas the if it doesn't air is not enough?

[tpeter]

Thanks for the info.

I'm heading to the junkyard on the weekend to try my skills on the throttle body And get that if it works correctly. I will post my results after it.

[tpeter]

No luck with the yunkyard. Just got two bonnet holding struts. As a quick solution we have added some carbon cleaner to the air intake, while the engine was running. I didn't see any smoke coming from the exhaust, so carbon might not be an issue or it didn't reach the throttle. Though it felt a little (I mean a little) more responsive after it.

I'm postponing the disassembly of the throttle body until end of Feb.

[JohnGD]

Since it happened 5000km after the timing belt change, I'd also check the timing mark alignment. The manual tensioning system on the 5SFE doesn't really do a good job.

So with the crank on 0 TDC, take off the top timing cover and check the cam sprocket marks. There are many examples in the DIY section. The belt may be slacking and causing retarded timing and robbing you of performance.

[tpeter]

JohnGD, I thought the tensinoning system is with the an idler tensioner spring? Is there something else? Unfortunately I couldn't watch the mechanic building it back on...
I might have something like this:
Gen 4 5S-FE Timing belt change - lost power?
The difference is that I bought a Toyota belt, directly from Toyota.

Fenixus, I have checked it multiple times, but my idle is near perfect. I have never thought it will stall. Can it still be the IAC valve?

[fenixus]

JOhnGD's point is that if the timing belt has been aligned just so so and old tensioner and spring were used, then there is a chance that improper tension was applied and belt could have jumped a tooth after a few thousand miles, it happens. that's why you should double check the timing marks if they are still aligned.
also try pin pointing the source of noise in garage or parking lot at idle, maybe just using throttle to make it appear.
you could use either a mechanics stethoscope or a 3/8'' vinyl tube to your ear or whahever you find works for you

yes, IAC could still be a problem and honestly it needs to be removed off the throttle body (and body off the engine first) to see it and clean it if necessary.

Also, IAC cleaning is problematic, even with it off the car, something may always go wrong ... so if it looks bad and you can't clean it good enough or there is anything wrong with resistance readings from motor then just replace it with a new one.

here is what I found in FSM regarding IAC and TPS cleaning:

NOTICE:
To prevent deterioration, do not clean the throttle position sensor and IAC valve.

in short those items call for replacement if there is ANYTHING wrong with them, no cleaning recommended, YMMV.

[tpeter]

I will check the timing belt with my mechanic. The tensioner and the idlers were both replaced, although I'm pretty sure that the spring stayed.

Will get back to these questions most likely after holidays.

ありがとうFenixusさん