Throttle response around idle area poor, almost stalls

[andrew_baran]

I recently swapped my m20 b20 out for a b25. I have some running issues around idle.

When the car idles, it runs ok. Bit tappety and I think it hunts a bit in comparison to the old engine, but not enough to move the rev gauge.

When I hit the throttle, the car is slow to respond, then struggles through the low revs before cleaning up in the higher rev range (3k plus).

On the way back down, the revs drop and the car almost stalls. It recovers, hunts and splutters a bit before settling down.

If I apply just a bit of throttle, the car hunts and misfires, and almost stalls itself.

When I unplug the AFM, the car is sliiiightly better responding around low revs. Not very much though.

I have checked for vacuum leaks around the inlet with no success. Everything looks good. Could it be either the AFM, TPS or ICV? The ICV and AFM were both off cars that ran well...

[zd3bx]

Sounds pretty similar to what I'm experiencing...

I created a thread myself about this last week > http://www.e30zone.net/modules.php?name ... c&t=239438

My air pipes look good too, so I'm thinking fuelling side of things, FPR, injectors or pump...

Haven't done anything myself yet, so the problem is still there.

[andrew_baran]

Very interesting. Symptoms are almost identical to mine. I bought a fuel filter today, and i'm cleaning my ICV and AFM too. So I shall report back any findings.

[zd3bx]

I replaced my fuel filter only about 5k miles ago, so won't be that.

Yeah I'll try cleaning my ICV and AFM this weekend too, and see how it goes from there.

[zd3bx]

Hey Andrew, a quick update for you - cleaning the ICV and AFM, made no difference to this problem, so it's something else. Let me know if you find out what's the cause.

[FinalD]

Have you guys tested (without removing) the throttle position sensor?

http://www.e30zone.net/e30zonewiki/inde ... ion_Switch

[Brianmoooore]

Throttle position switch, either not working or badly adjusted, air leaks and injectors in need of a rebuild. Probably contributions from all three.
Another less likely cause is a duff AFM - test it rather than replace it blindly. (I assume it was replaced as part of the conversion?)

[zd3bx]

I haven't touched my TPS yet, so that could be it...Thing is, testing/cleaning it sounds a bit too technical for my expertise lolz

EDIT: After some Google'ing, found this thread > http://bmwe30network.net/forums/read.php?3,7197

Seems like it is the TPS.

[ah]

I've got the same problem and have had for about a year and half.I tried nearly everything other than a brand new AFM and a brand new set of fuel injectors.Mine coughs and pluters at 1500rpm.

[Morat]

What MPG are you getting?

Get your multimeter out and check your blue temp sensor. There is a whole checklist in the wiki, Blue Temp Sensor was my problem coupled with (aftermarket) HT leads which were reading well over 6k ohms. OEM HT leads last very well by all accounts.

Those two changes took me from 18m/g to 21.5m/g average on the OBC, cleaned up my idle and sorted the off idle throttle response. I had already checked for air leaks, but found none.

[Brianmoooore]

I haven't touched my TPS yet, so that could be it...Thing is, testing/cleaning it sounds a bit too technical for my expertise lolz

EDIT: After some Google'ing, found this thread > http://bmwe30network.net/forums/read.php?3,7197

Seems like it is the TPS.

Apart for them thinking an AFM is the TPS for about half the thread, until Ferdinand came along, that thread covers it quite well.
The TPS must work, and be adjusted to switch off the idle map as soon as the throttle leaves its stop.

[zd3bx]

Morat, I mainly do short city travels, so I get about 20 mpg. My leads are only a few months old, made by BBT - seems to be a decent make, but the aforementioned issue was there with the OEM leads as well.

Would it be a good idea to unplug the TPS to test if that cures the problem? Assuming it's the cause, then there should no longer be any hesitation when slightly revving the engine from idle?

[Brianmoooore]

Unplugging the TPS will simulate a fault with it. If unplugging it makes no difference, then it could be an indication that it's faulty.
There should be a sensor threaded onto plug lead #6, which is rarely present on aftermarket leads. Lack of it won't cause your problems in their entirety, but won't help.

[andrew_baran]

I've actually left my car as-is for a while. I had to just shove it all together to get it through the MOT, and since then it's been improving with mileage. I've been getting close to 30mpg on a run!

I unplugged the TPS when I was having the issues before, and it just made the response worse, and the car ran very rough. Leaving the TPS plugged in but unplugging the AFM sliiiightly improved response, and unplugging the ICV and AFM sent everything to sh!t, as expected!

[zd3bx]

Tried unplugging the TPS this morning, but it made the idle very rough and the struggle was still there, when pushing the throttle a little.

Will try unplugged AFM, see how that goes, but yeah, it's not a big deal - just a bit annoying ;)

[AdamBeevers]

May seem stupid but mine done this when I was unplugging sensors, I think it put a code in the ECU or something as I unplugged the battery and left it for a few days and now she's a dreamer