Bouncing revs on idle, kagarooing etc

[Barton]

Recently, maybe since the engine was fitted/rebuilt

most of the time when i start the car up initially, the revs bounce up and down between about 500 and 1k rpm

when the car is under a tiny amount of load with the throttle just on, the car will kangaroo, it will also do this when i try and use the engine to slow down

it also seems to want to drop the revs too low when i lift off the accelerator, once or twice the car has actually stalled (this is more at low speeds like turning round in a carpark / dead end road)

any ideas?

i'm guessing a vacuum leak/faulty icv

but obviously during the rebuild, a lot of seals/gaskets were replaced, and i gave the icv a good blast through with carb cleaner

i haven't yet checked the emmisions, so the idle mixture on the AFM might be a little off

[eltel]

do all your basics, check mixture, check for air leaks on the inlet side and around cam cover.
check all the electrical connectors are fitted to the correct items and are fully connected
then make sure your tps just clicks as you move the accelerator off it's stop on top of the inlet manifold.

check the multiplug connection under the inlet manifold is fully clicked in and as it should be, you could try wiggling it with the engine running to see if it makes any difference.

how many miles have you done since the rebuild?

when i rebuilt mine and got everything to spec it idled like a dog for about 25 mins, then all of a sudden the ecu remembered the right settings and ran like a dream

[suhinaffy]

My M44 E36 had this problem, It turned out to be a faulty maf sensor, I'm guessing since you have an AFM, you wont have a MAF.

[eltel]

Barton..i assumed in my post that you had and M20 320 or 325..that is correct isn't it??

[Barton]

yeah m20b25

done a good few miles

seems to be worse in cold weather, but that may just be coincidence

[eltel]

Maybe worth testing your blue temp sensor

[e30topless]

check that the ICV is buzzing away when the ignition is on, and clean out the TPS

[m_jermyn]

My bet is a air leak.

Check every rubber hose around the air flow meter and throttle body. Also the hoses that lead to the brake booster and up from the cam cover to the throttle body...

[eltel]

see if the rubber blanker is fitted under the throttle body just behind the tps, you need to bend your arm in 3 places to get at it without removing the rubber inlet hose etc but you can feel it

[Barton]

the blue temp sensor is new

the oil beather from the rocker cover is new

the rubber bung on the bottom is there


will check the icv tomorrow

the tps clean, i presume you mean remove, and dismatle it? as for the positioning, i've never really heard an audible click on either engine as i open the throttle

air leak is plausible, hope its not inlet gasket, unles i just try and tighten it up

when i refitted everything, i did re-clamp the hoses to the brake vacuum

the main elbow is new, although it is one for a 2.0 stretched to fit the 2.5 t/b

[eltel]

you should be hearing a click just as you move the throttle of it's stop by hand, that is what tells the ecu to run it's idle map.

has someone adjusted the small threaded bar that the throttle rests on to increase the idle??

to check your inlet gasket spray wd40 or carb cleaner around it and see if the engine revs

[Barton]

the idle may have been adjusted, but then is there aver a perfect position for the butterfly to be in before i start playing with the tps?

[kman82]

There is a sticky at the top of technical and has tons of info and tests for you to try first...

http://www.e30zone.net/modules.php?name ... c&t=153524

I had similar symptons with mine which turned out to be a split in the hose going to the fuel pressure regulator (correct name?) at the front near the air filter

[Barton]

yeah, thats a new hose too, doesn't appear to be leaking

icv is buzzing away

[Barton]

i sprayed all the hose joins with carb cleaner and nothing changed the idle

i checked the tps - no click

turned the idle screw back and i think i was able to hear a click at the very bottom - but - when i took it out for a drive everytime you dropped the clutch, the revs dropped too low and the car stalled.

i've had to screw in the idle screw again, i'll have to take the t/b off at some point and clean and rest the tps with the screw in its current position.

also found one of the exhaust manifold studs had almost completely unscrewed itself from the head so tightened that back up and nipped up the other studs, sounds a little less ticky

[Barton]

forgot to mention, when the revs are bouncing at low speeds/idle the mpg gauge is going mental

[eltel]

you need to follow the motronic blog at the top of this forum..get everything back to how it should be.
sounds like your mixture maybe out slightly amongst other things.

the car needs to idle with the tps just clicking as the throttle moves.

[kman82]

Someone else might be able to comment on the mpg guage but from memory mine goes back and forth when you start and stop.

If I were you i'd get that TPS off, give it a good clean and get a multimeter on it as the clicking can be misleading.

I havn't done it myself but that other thread details a procedure for setting the idle screw position. I believe it may need special testing equpiment up the exhaust to set it correctly???

[eltel]

bmw use a special blanking tool for the icv, one way i was told about is to bridge all 3 connections on the tps plug so that the ecu doesn't mess with the idle.. then adjust the idle screw to 750-800rpm.
re-fit the tps plug then slacken off the idle screw so that you get the click just as the throttle moves off it's stop.

it improved mine slightly may help yours.. but not 100% convinced it is an approved method

[Barton]

but surely slackening off the idle screw defeats the object of turning it up?

[eltel]

yeah thats what i thought but it did improve my idle surprisingly... you have to disconnect the tps and bridge the wires though so that the ecu doesnt meddle with things..i will try and find the thread i got this from

[kman82]

It's all in that link i posted above

[Barton]

yeah, but i dont understand when the plug is bridged, disconnected etc

and would it not be better to re-position the tps once the throttle stop has been adjusted?

[eltel]

yep cheers kman.. it was from the motronic blog..cut and pasted below

Adjusting the base idle speed and mixture

First, make sure everything else is up to spec (check sensors, ignition, air leaks, throttle, TPS, etc.) before messing with these settings. The factory settings should be pretty much spot on, perhaps a little lean if everything is working fine.If that’s okay, warm the car completely, and unplug the TPS connector and short all three pins together. This instructs the ECU not to ”amess”a with the idle speed and sets the the ICV in a nominal position.

Start the engine and adjust the idle with the bypass screw on top of the TB. Try to set it to around 800rpm. Rev it in-between adjustments, as sometimes the adjustments don’t have an immediate effect. If you can’t get the idle up high enough, your mixture is too lean, so you need to dial in some with the bypass screw on the AFM.

Adjust the mixture in small steps (wait about 30seconds each half turn for the computer to ”˜catch up’) to obtain the so-called ”abest high idle”a, which means that you stop enrichening the mixture as soon as the RPMs stop rising when you do so. Now, lean it out 1/4th of a turn again, this should provide an ”aabout right”a mixture. Next, rev it up to about 3000rpm and quickly close the throttle. If the RPMs drop briefly under the set idle RPM and then come back up the mixture is too rich and you need to lean it out a little more.

If you can’t turn the screw anymore (usually inwards/richer) and still haven’t reached a correct mixture, the AFM spring probably needs adjustment. Turn the screw to approximately half way, open the AFM and adjust the spring one or two notches either way (clockwise is leaner, ccw is richer, exactly the opposite of the CO screw), until it runs better, then make final adjustments with the screw.

If you think you’ve got it right, plug back in the TPS and take it for a spin, and make minute adjustments to your likings.

It’s probably wise to check with an exhaust gas analyzer (drive by your garage or a service shop) afterwards if the CO is within spec (0.5-1.5), but following the above you should be able to set the idle pretty much to spec without.

If you can’t get it to idle correctly this way, you have another problem. Most likely your valve clearances are set too tight.

[eltel]

when i finished the above proceedure on mine, i tweaked the tps slightly but due to only a few mm of adjustability i had to back off the idle screw slightly to ensure the 'click' came in at the right time.

[Kieran_n22]

my car hass exactly the same problem! I changed the ICV but it's got worse if anything!

[Ajsingh]

I just done a 2.7 conversion on my 325i and it idles nice but you can hear the revs slighty going up and down. And at low speeds it kangaroos. I dont know what to do and need help!
Sorry for 'nicking' your thread but we have similar problems

[eltel]

sorry for throwing this in to confuse the issue even more..but the kangarooing at low speeds could be a slightly different problem to the idle issue.

i remember a thread a few years back dealing with the kangarooing at low speeds and around town, if i remember correctly someone put it down to some slight backlash in the drive train..gearbox or diff i think.

i had this problem with a 320..it was a nightmare around town, when i put a 325 in it i also put the 325 gearbox and diff on. it totally reduced the kangarooing problem to nothing. it may have been a coincidence but certainly made sense at the time.

[Faz2kool]

Mine is doing the same thing. I've had a replacement 325 engine fitted and was running fine for 100 miles and now starts to jump revs and then cutting out. It's currently back in the workshop but someone suggested to replace the dizzy cap and leads. Could this be it or does that have nothing to do with it bouncing revs.

Sometimes whilst driving, it refuses to pick up speed also. Temp gets hot within 15 min. Not sure why.

[Ajsingh]

Iv been told to adjust the co on the afm but i need a co machine to do so

[eltel]

Faz2cool... check the crank position sensor cable for chaffing where it goes behind the pulleys and check for burn marks if it has been routed close to the exhaust manifold..

also wiggle the multiplug beneath the inlet manifold with the engine running and see if it alters the revs/running at all. check it for a bad connection and make sure it is tight

2 common causes of bad running that are easy and free to check before spending money!!

[Faz2kool]

Thanx eltel, will do this later today.

[ETERNITY]

I had this problem and have altered the afm screw and the adjusted the setting inside the afm internals and its idling ok and stoped kangarooing.

will get the co checked next week when I have my MOT, so might have to adjust the afm screw to set it to 0.8% and 400ppm.

[ETERNITY]

Is there a diagram/procedure to set up the tps on the zone somewhere

[kman82]

Try the sticky here....

http://www.e30zone.net/modules.php?name ... c&t=153524

Nice looking motor mate