View Full Version : Lumpy Idling leading to stalling.

April 3rd, 2005, 04:07 AM
I recently replaced my engine due to rod knock on the previous one (which ran fine i.e. idled nicely at 700rpm's, no fluctuations) but since getting the new engine in and running it doesn't idle too well. It'll just fluctuate between 300 and 600rpms before coming to a stall. It also sounds like it's missing occasionally but it runs fine higher up the rev range, absolutely fine!

I've tried changing the spark plugs, leads and idle control valve (even though i was using the old intake manifold from the previous engine), but still no joy. I presume the dizzy has a rotor arm which i was trying to get at but unfortunatelly the bolts are tight as buggery! i've got a spare dizzy there from the old engine but didn't want to swap them in case i messed up the timing.

All my vacuum lines are in the correct place and are all ok condition-wise, i don't think i have any leaks in the intake manifold that i can hear.

Any ideas? it's just a bugger trying to keep the revs around 1k when approaching a junction.

April 3rd, 2005, 05:09 AM
air flow meter? just a guess

April 3rd, 2005, 05:18 AM
Well i just checked it according to the TSRM thingy and it turned out ok..

it's reasonable cold outside and here are the results:

E2-VS = 261 ohms
E2-VC = 280 ohms
E2-THA = 3066 ohms
E1-FC = Infinity/Zero

any other ideas?

April 3rd, 2005, 05:57 AM
leak on the intake manifold? how were the gaskets?
can you hear any leaks?
try using engine start/ether and spray it around the manifold, if ur revs pick up in a certain place you spray... theres ya leak (but you probly already know how that works lol)
ignition timing? whats it set at

another guess lol

April 3rd, 2005, 06:07 AM
Well i can't hear any leaks on the inlet manifold and i did have it off the other day as well due to changing plugs and leads etc. The gaskets aren't new but they're in good condition. I'll try your method of spraying it to find any leaks later on and see how i get on.

I never removed the distributor from the new engine so it should still be set ok, i need a timing light to check don't i? hmm, i'll see what i can do with that.

April 3rd, 2005, 06:45 AM
Checked my diagnostic codes. I didn't have an Engine light on but i thought i'd check anyway.

I had a code 24 - Air intake sensor. Checked about for one but i can't see one? am i blind?.

I reset the ECU ans now it blinks constantly, no more errors?

April 3rd, 2005, 06:59 AM
If it blinks constantly with no pauses it means you are fine. Your ECU is saying, "No codes for a change. No codes for a change.":)

April 3rd, 2005, 07:23 AM
yup, good! still got a dodgy idle though lol, not so good!

April 4th, 2005, 05:25 PM
well i changed my dizzy over today and cleaned up the contacts and rotor arm edge a little before reinstalling it. Still idles dodgy.

The funny thing is it seems to idle worse as it warms up to normal operating temperature, even at the same RPM's. like.. 700rpms cold it idles not too bad but 700rpms warm and it'll jump up and down a bit then stall.

Again i searched about for vacuum leaks today, none. Searched for manifold leaks, no difference although i haven't tried Engine Start or the likes yet.

I don't suppose having one of my downpipe bolts undone (blowing a bit at the flange) would cause it to idle like this?

Engine seems ok, no loss of oil or water, no spikes in temperature or gradually lower oil pressure, no milky oil, don't think i have any problems there although i will do a compression test at some point.

Another thing, it seems to burp/missfire occassionally anywhere under 1000RPM's.

Anymore help appreciated lol :)

April 5th, 2005, 02:27 AM
hmmm... did you unplug ur afm with the battery connected recently?

code 24 usually suggests a problem with the afm... see if anyone lives locally and borrow theirs

April 5th, 2005, 02:46 AM
Three things to check, that I can think of, in addition to SG's ideas.

Dashpot on the throttle linkage... make certain that is set correctly. Throttle postition sensor setting. And check the ISC for a vacuum leak - a leak or faulty sensor here will give you a dodgy idle for sure.

April 5th, 2005, 03:44 AM
the AFM was unplugged with the battery connected, i tested it with a multimeter and reset the ECU and the code hasn't appeared again.

I've tried adjusting the dashpot several times but didn't make any difference, so i returned it back to the original place.. is there a proper way to adjust these?

Throttle position sensor wasn't adjusted and it's the same manifold/throttlebody i was using before with no problems.

The ISC shouldn't have any leaks, nor should it be faulty as i've replaced it with another one, then switched back again, but whenenever i unplug the electrical connector to it it doesn't seem to affect revs at all.

April 5th, 2005, 11:39 AM
i'm having the same problems with my lex/550 setup.. i believe my afm is on death row

April 6th, 2005, 07:05 AM
well part of the problem was the last 90(ish) degree bend rubber hose that connects onto the throttlebody, it was a little mullered so i replaced that and it's idling a little better, no stalling *cool* so i'm almost there... ach!

April 6th, 2005, 11:46 AM
well part of the problem was the last 90(ish) degree bend rubber hose that connects onto the throttlebody, it was a little mullered so i replaced that and it's idling a little better, no stalling *cool* so i'm almost there... ach!

Check I/C piping
Check timing
Check CPS (I was a tooth off on mine, and it fixed it)
Check all vacuum lines for leaks
Back screw out on Lexus AFM (worked for me as well)
Adjust fuel pressure (If possible)

After checking all of those and waiting a few days, the ECU re-learned everything and idled beautifully. Hope yours gets up and good soon :)


April 6th, 2005, 05:40 PM
i think i've found the problem although i haven't replaced the faulty part yet. I unplugged the vacuum feed going to the fuel pressure regulator and it idled nice at low RPM's, just how it should, no fluctuating or missing. I've been led to believe that it's a faulty VSV (probably stuck on the inlet manifold vacuum at low idle?, instead of atmospheric pressure?)

i will replace it tomorrow as i have one from my old engine.

So do these engines run with a two stage (speed) fuel pump system? where at idling range it'll only flow so much therefore the FPR will need to be disconected so to speak to keep fuel in the line and then the pump switches to it's faster speed and the VSV switches over to inlet vacuum feed to allow the FPR to operate again like any other EFI system? or am i just wrong lol..... Also could it be that the VSV is fine and that it's another problem like dirty injectors? i don't think it's the fuel filter as the old engine was running fine apart from the knocking.

Another thing, the vacuum tank for the ACIS (i think) system, there's one vacuum line in the back of it (going by touch) and there's another nipple on the side of the can, do i leave this nipple naked or do i run another vacuum feed to it?

April 6th, 2005, 07:29 PM
how long ago did you swap the motor out?? If it was just recently it could be that you are low on coolant or thier is a air pocket trapped in the motor causing the coolant temp sensor to do weird things..

April 7th, 2005, 02:07 AM
last week but the temp sensor for the guage seems to be working without any erratic behaviour so i would assume the ECU temp sensor would be reading ok too.

going to change the VSV today so i'll let yous know how i get on.

thanks for the great help and ideas!

April 8th, 2005, 06:16 AM
well i fixed the problem today! yay!

it was the simplest of things, yes, a leak in the intake manifold where it joins the runners. Even though the gasket is good and the bolts are torqued up properly it was still leaking. A little squirt of Engine Start and it revved a bit so i put some pikey instant gasket on it to seal it, works a treat.

Also on a side note i got some Toyota Red Coolant today and sorted that out once and for all, no air pockets in the system!

One fine day for the supra!

thanks for your help once again, especially suprragirl (hope that's right) for the Engine start idea!