Engine rev problem

[davey]

Hey everyone.

I own a manual 2000 ford fiesta, and the engine has a problem to do with revs. It idles just fine but if i touch the throttle and let go it likes to rev upto 3000 rpm and hang there for a second or two, then drop back to idle. This happens when driving also, for example when i change between gears and dip the cluch the revs drop then go upto 2000 and hang there for a second OR until i have changed gear, then it carries on as normal.

I have cleaned the Idle air control valve with brake cleaner and rag, and i have tested the resistance and it came out at about 43ohms. I also tested the voltage of the Throttle position sensor (with the ignition on – but not the engine) and the signal wire was saying .94v and as i opened the throttle with my hand it increased slowly to 4.8v which seems to me to be spot on.

There is also a Power steering pressure switch which i know about, that is known to cause this rev issue, but i’m not sure how i would test that.

I hope i have explained clear enough and that you understand what i mean. I do tend to ramble on alot before letting others speak haha.

All advice is appreciated 🙂

Topic

[EricTheCarGuy]

I’d be checking the throttle cable to see if it’s sticking. Try disconnecting the cable from the throttle body and rev the engine. If it goes back to normal right away check the cable for any tension or drag, if you have any replace the cable.

[davey]

Thanks Eric. There seems to be no resistance within the cable itself, and the throttle body springs back as soon as you let go. I have started to notice how the revs hang as soon as i let go of the throttle, such as driving along and letting go of the accelerator and i can’t feel the car engine brake for a second or two then i feel the resistance of the engine braking.

[EricTheCarGuy]

You might want to check to see if something is obstructing the gas pedal then. I’ve seen instances where floor mats cause the pedals to bind. In short I think you’re looking for a mechanical issue, I’m having a hard time coming up with causes that would be electronic in nature because the throttle has to be open or stay open in order for the car to accelerate.

[davey]

I have investigated under the pedal and i there seems to be nothing out of the ordinary, and i dont have any mats for this reason among many aha! I understand where you are coming from i myself was thinking it has to be mechanical as the throttle is cable and not electronic it. The throttle body does spring back immediately after release, as does the gas pedal (even without the cable attached to the throttle body!) It doesnt have any codes, and it has no engine light on at all.

A few people i have spoken with agree in my suspicion of it being the TPS, but like you say in your videos, there is no point in throwing new parts at it until it is confirmed what lies at fault.

For the time being i have arranged to take my car into college Thursday and dive deeper into finding the cause. I appreciate all the help you have given so far though Eric, and i shall update as to what the outcome is. 🙂

[ytram]

Dave this is a wild thought! The Saturns would have this problem also. TPS would sometimes for what I understand was base of the problem, and a blocked passage or carboned up IAC.
Strangely on my moms car, it turned out to be engine temperature not warm enough and or computer not getting correct signal to know engine was right temperature.

[dreamer2355]

This was a video on a similar issue.

Let us know what you find out 🙂

[davey]

Hey guys. I would like to say thank you all for your help! On my way to college last Thursday the engine light illuminated on the dash, so there was no better opportunity to plug in the diagnostic computer. The computer found the code “p0240 – catalyst efficiency below threshold”. I reset the code, as we believed it was caused by the idle problem, and it has not illuminated since *touchwood*. It did not bring up anything of why the rev problem was occurring and i have since replaced the Idle Control Valve which made no difference. It began revving itself right up to maximum with no one touching the throttle (i switched the engine off immediately). I removed the entire intake manifold today and discovered that a vacuum pipe elbow joint seal had broken apart, and the pipe had become dis-lodged.

All this because of a loose pipe!!!!

This leads me to reveal that we are running perfectly at last!! :cheer: :cheer: :cheer:

[college man]

thanks for the update and the fix. banana:

[dreamer2355]

Nice job on finding the issue 🙂

[EricTheCarGuy]

Thanks for posting the fix. Yes vacuum leaks can cause all kinds of issues like that, well done finding it. Thanks for the update and for using the ETCG forum.

[Author]

Replies