car revs too high on idle

[T1BBST3R]

Hi folks,
Well, after getting my car back from the garage after the engine wouldnt rev enough at idle for the shit to move below 2.5k, now it pulses on idle at between 1.2 and 2.5k revs!!! Not only that, but sometimes it idles slowly from whatever revs i pull the clutch out from up to 3k revs at junctions.

Bloody thing! I have a new o2 sensor from the mechanic and a proper maf sensor (well, oem) , I am thinking it is the throttle position sensor which will order in the morning but would like to hear if anyone actually knonws, 'what the diddly-yo!'.

It pulses on idle from 0.8 to 2.5k revs, or slowly rises to 3k revs on idle, sometimes I put ignition on and see the rev needle pulse to 3k also before cranking the key.

Was hoping would be ok after getting back from shop, is not the only problem, sometimes it (he) goes over bumps and the engine cuts out over bumps, making the instrument panel go dead but a tap on the ingnition barrel fires him back to life because the engine also cuts offf.

The high idle (especially in the 10 mins of traffic out of Lincoln) has nocked around 40 miles offf a tank of fuel.

Throttle position sensor is going on now anyway, could it just be that the computer hasnt been reset from the last problem because the 'vehicle recovery' workshop couldn't reset the computer? Its the symtec 56 with built in immobiliser/central locking fob model.

[Robsey]

Resetting is just a matter of disconnecting the battery for 5 minutes.

Connect back up, and the car will re-learn to the current configuration.

The high revs - is this when cold, or all the time?

It could be the engine coolant temperature sender telling the ecu that the engine is could, thus increasing fuelling.

It could be the trottle position sensor.

If the revs are rising and falling in a regular manner (hunting), then it could be a poor mixture. A likely cause could be an induction leak or vacuum leak.

Is the air intake trunking okay, or is there a split in it.?
Any loose or cracked / split vacuum pipes.

Look at the simple / cheap parts first and work your way from there.

[ilovedmymantas]

I had a similar sounding problem a while back (self-inflicted) that might be a contender.
tps is also mentioned in the post

viewtopic.php?f=15&t=13780&hilit=speed+sensor

The paperclip test should help determine what's wrong, try that first.

viewtopic.php?f=31&t=630

[T1BBST3R]

Pretty sure hoses are all fine, not sure about induction that's a pipe that goes before the air filter isn't it?

Also, sometimes when ignition first goes on, the rev counter pulses to about 2.5k then back to zero before the engine goes on. Sometimes it wants to idle at 3k, sometimes will pulse between 1.2 and 2.5k.

Shame cant test the throttle sensor really because the plug doesn't expose any wires.

There is no eml and as for speed sensors, the brake pads were changed recently, could a bit of dirt over one cause this kind of problem?

Did the 'paperclip' thingy. The eml light cut off for a bit (car does that sometimes) and lost count. Only know that after the start up sequence it goes over 51 additional 3 flash sequences.

Problem did start as it not idling enough, the revs would drop to 200 and then pulse back up to normal (sometimes with a little help from the throttle), thought this was the maf.

[Mk3alan]

My intake pipe was split on the CD, didn't see it at first but it was falling in half in the bottom of one of the convolutions!

Alan

[T1BBST3R]

will take all the air pipes off and have a proper look. Isn't there a test you can do with your hand over the oil filler cap? If there is no suction then there is a vacuum leak, or has somebody just made that up...... >Think is something to do with the camshaft area breather hose to throttle body on x20xev engines.

[Robsey]

Hmm - if there was going to be a vacuum, it would be from the breather pipe to the throttle body.

The oil filler hole does not give off a huge amount of air, but would have a bit of "expelling air" from the crank case breather. There should definitely not be a vacuum.

If I remove the cap, it tends to allow oil to be spat out everywhere.
If there was a vacuum, this would not happen.

Higher than normal idle would normally result from a faulty idle control valve or engine coolant temperature sensor.

First to check / change is the coolant temperature sensor.
The one with the square two pin connector.
These are very inexpensive to buy.
Just a bit of a fiddle to get to due to the location of the alternator and drive belt.

Second would be the idle control valve.
These have always been problematic on Cavalier engines.
They are very oily engines, and the control valves get clogged or gummed up with old engine oil vapour. (Along with associated pipework).

You could clean the whole of the breather system pipework, and also do the control valve whilst you are at it.

Replacements are quite expensive, so do as much as you can to check all other culprets before splashing your hard earned money on a new idle control valve.

Unfortunately if the idle control valve is the issue, replacement is the only long term solution cleaning usually only gives a temporary fix - a couple of months is normal.

[T1BBST3R]

Thanks,
got 2nd 12 hour shift day tomorrow so will have to wait until Tuesday..... Got a temp sender reserved for Wednesday at my local GSF with rediculous 80% discount just in case. They are like carpet shops those places.

[T1BBST3R]

Checked over air pipes, found a scale like crack / pertrusion in the back of the maf case from something.

Has been patched over with a puncture repair and gaffer tape.
Wasn't sure about whether the ribs on the air hose to throttle body so put a load of bycicle glue in all the cracks there to see if that helps.

Also,
[img][img]https://farm8.staticflickr.com/7925/33042213548_342edc2017_q.jpg[/img]IMG_20190129_122455 by terry_tibbs2012, on Flickr[/img]

Could this also cause the problem? The red wire came unattached.
Also, which one does the ignition light as I think there is a break somewhere in the loom which makes the engine cut out. When engine is cut out I can put the clutch in see and then all the bulbs come on except eml. Pull clutch out again all goes dead until I bash the ignition switch to get the eml light back.

[Robsey]

Took me a while to suss out that black / purple wire. It looks like a "W" contact, so live whenever the key is in the lock.

A quirky mod, but never an original wire on the cavalier.

Only possible on the really late cavaliers with the Vectra-B style ignition switch.

I did an ignition switch pin-out here.
One of my incomplete projects to add accessory live to the more common ignition switch.

viewtopic.php?f=21&t=4069&start=1575

Scroll down near to the bottom to get past my infotainment waffle.

[T1BBST3R]

Thanks,
car does still pulse from 1.2k to 2.5k now but doesn't get up to 3k anymore. Got the temp sensor today although will have to wait for the weekend now to fit it. will give me an excuse to try to find where a little trickle of coolant leaks out of the front of the radiator somewhere too unless it's too cold. seems to say it runs at just over 90 degrees, don't know if thats because it's colder this time of year, should be at 97. At 100 degrees in traffic the fan still comes on and cools me back down to 95 again which is good(don't want the expansion cap blowing off).
Will also see about checking the number 50 and 15 ignition wires, hopefully without taking the dash off as don't want to spend a whole weekend on a hunch.
Thinking ahead, one of those dewalt heated jackets would be nice.

[tom50]

Mine sometimes when the engine is warm but not hot enough for the fan to kick in, when driving the idle speed will increase to 1000-1300rpm until the car stops rolling, which can be a pain if in slow moving traffic, haven't a clue what that could be, ???