Throttle lift delay

[JGood]

I've noticed I have a ~2 second delay when lifting the throttle before RPM's drop. Say I'm cruising a 3k RPM's. I lift, and it will stay at 3k for ~2 seconds, then start dropping like normal (or like my m20 did, I should say). This makes for inconsistent shifting... and it does it at any RPM's. I can see this being a huge issue when going 10/10ths and heel-toeing into a corner, when you DON'T want that extra 2 seconds of throttle input.

I did some searching on bf.c, and it seems like several people have the same issues.

Now the throttle is mechanical, the IAC can only control things up to 2k RPM's or so, what else is coming into play to cause this? I've heard its emissions related, but I just can't figure out the physical means in which the engine holds that RPM, whether controlled by the DME or not, as there is just no way to hold the throttle body open on these motors.

The car is an 85 325e with a 95 m50tu if anyone is curious.

[devonjordan]

Maybe the cable/butterfly is sticking? Clean it up and check the cable?

[hugh jass]

when you operate the throttle plate on the throttle body manually does it stick open and close slowly or snap close quickly?

[JGood]

No, its snaps closed, the spring is strong. This is definitly not a malfunction of the throttle body.

Plus, this is something many other people have experienced. This is a long delay, it really is ~2 full seconds, and it keeps the rpm's exactly where they last were. So if you go full throttle, from 1k to 4k, and lift at exactly 4k, it will remain at exactly 4k for 2 seconds. If the throttle body was sticking, it would continue to climb RPM's.

It's hard to get help on bf.c as those guys believe its clutch related and just accept that fact. The common theory seems to be the clutch switch triggers the ECU to do something with the DME and injectors and blah blah blah. My thing is, I don't even have a clutch switch, and you need air to keep RPM's up... where is it getting the air from if the throttle plate is closed? I don't see the IAC moving enough air to keep the engine at 6k for 2 seconds (yes, it does it that high in the RPM's as well).

[hoveringuy]

I can tell you that it will sustain 4k rpm with the throttle body completely closed. While I was developing the Hall sensor conversion I ran into a wall at about 4k where it would self-sustain there for about 5 or 6 seconds with the throttle body completely closed. It had to do with an excessive gap between the sensor and the teeth. Not the same sypmptoms as yours, but shows that the motor WILL run at high rpms with little/no air!

[JGood]

No shit? That's wild. It could very well be ECU controlled then, for emissions purposes. I just find it hard to believe that:

1. Not all m50's do this
or
2. Not everyone notices

It's not a huge deal, but for a track car it would be a bad thing.

[hoveringuy]

I shit you negatively.

[lennon]

i dont think its a malfuntion of anything. from what i understand, later m50s (i think it came with vanos, my pals non-vanos m50 does not do this) and all m52s (and perhaps other motors) do this as an emissions control feature so that the car doesnt backfire or anything between every shift. i think it is dme controlled but i dont know the workings of it. i know some people with m50tu's and m52s and it can be weird to drive. i wouldnt want it.

[mattdk318i]

my 95 m50 does this, It drives my Fiance' crazy. She swears theres something wrong with it. But it runs perfect other than that quirk.

[etxxz]

a heavy ass flywheel will do that

[m3_eater]

My M52 doesn't do this, but the same engine in a 1998 E36 328is I once had did. Drove me bonkers. A lighter flywheel helped, but I don't recall it completely resolving the problem. The clutch delay valve also pissed me off to no end - nice getting rid of that once I learned what it was! Are you running the ZF 5-speed?

[JGood]

No, I'm using an eta transmission/clutch/flywheel (single mass and shaved). This is absolutely not caused by a heavy flywheel. It stays at the exact RPM then instantly drops. It's not a gradual thing. It is most definitely a controlled feature.

However, I went for a drive today and tried to get it to NOT do it, and I was successful. It seems like it does it under normal driving conditions mostly, when you start playing with blipping the throttle and stuff, it won't do it all the time. This sucks, my track car is an m20 and my daily driver is an m50, so if I get used to one I'll surely fuck up the other.

[Axxe]

A lot of modern cars do this for emissions. Maybe a chip will cure it?

[JGood]

A lot of modern cars do this for emissions. Maybe a chip will cure it?

I have a Dinan chip in it. Good idea though, thanks!

[SpecM]

my friend's mk5 jetta 2.5 does this. I hate it, on WOT near-redline upshifts, make shifting all clumbsy