Laggy throttle response

[skuyler]

I drive a 5 speed '90 325i sedan with 168k on the clock.

I haven't driven any other E30s, but I have driven a few E36s. Now, I'm not sure if it is normal, but if i have my foot off the gas then depress the pedal, there is probably close to a half-second hesitation before the engine realizes I want to rev, and then it picks up like normal. The E36s I've driven (94 325i & 95 318is) get revvin' right off the bat, and that is a much more motivating feeling. Also, once I'm already on the gas, increasing it doesn't have any hesistation. I've read here before that it is just something we have to deal with, but is it really supposed to be this bad? I mean it is always throwing my rev-match downshifts off because of the lag.

I'm not much of a mechanic (see: oblivious), but could it be fuel filter or fuel pump related? I'm having other problems with those right now as well...Would it be worth it to switch to a lightened flywheel (would it change anything)?

Thanks.


Hey, this will be a lot easier, here's some video



Or

http://www.youtube.com/watch?v=1wlJ13I5LZg

[JGood]

That's not normal. A throttle cable is a throttle cable. They all swing the throttle body flap open, allowing air in, and the ECU adjusts fuel to compensate. Unless your ECU is from 1910 (read: non-existant), it happens so fast you don't realise it.

Drive by wire cars are different.

Something is wrong with your car. Possibly fuel filter. Give it a tune up. Check the throttle linkage to make sure nobody installed a rubber band in place of the cable.

[jlevie]

A bad AFM can cause this.

[skuyler]

oh yeah, i forgot to mention that in the last 7 thousand miles i've put in new"
plugs, wires, distributor, rotor, timing belt, water pump, and cleaned the throttle body...

and if i'm under the hood and pull the throttle cable to rev it, the throttle will open up, slight pause, then it'll rev, so i don't think its the cable

[jlevie]

Since you worked on the throttle body, is it possible that the TPS is misadjusted? The idle switch in the TPS should open when the throttle arm is 0.020-0.060" off the throttle stop screw. If the DME thinks that the throttle is still closed because it sees the idle switch closed that might cause a hesitation. Otherwise I'd say it sounds like the AFM.

[euroshark]

TPS. If you dont have a book, get one. That shit needs to be adjusted...If you barely give it any gas, what happens?

[skuyler]

Just a little? It hesistates a second then blips up the normal amount, depending on pressure...The hesistation seems worse if it is "coming down" from revs and i try to get it back up. It will drop a few more until it remembers that it is time to rev...the throttle body will be open before the car "realizes" it is go time.

With that description, should I check out the TPS and AFM?

[jlevie]

Yes. The Motronic system can only tell that it needs to inject more fuel by knowing that the throttle has been opened (TPS idle switch opens) and by the increase in air flow into the engine as measured by the AFM. So those are the logical place to start for this sort of hesitation.

[NC325iC]

i think hes exaggerating and its a normal amount of hesitation,
but to help out some i would go ahead and clean the AFM

[skuyler]

checked out the AFM & TPS today...My Chilton's manual wasn't very clear about continuity and such with the TPS, but after dousing each with carb cleaner, the car seems a little better, not exactly "of my dreams," but better...

thank you guys for all your help, i greatly appreciate it

[More&Faster]

i think hes exaggerating and its a normal amount of hesitation,
but to help out some i would go ahead and clean the AFM

doubt it. i have the exact same problem. at idle i can stomp the pedal to the floor and it's atleast half a second before the engine does anything at all. same thing if i flip the throttle by hand. i cleaned out my AFM and that wasnt it at all as it was perfect. i'll have to try my TPS next.

[NC325iC]

i know youre having the same problem, i said i think you are exaggerating the severness, its an inherent problem of the flap style afm it takes say... half a second for the air to push open the flap and then the engine realizes it needs more fuel and then vroom. it can be worse if the flap is having trouble swinging, clean your afm better, dont just spray at it, maybe wd40 a little when your done cleaning it

i woulndt spray anything at the TPS as this is an electrical sensor and not really a mechanical peice

edit: and get a BENTLEY manual chilton is a POS

[jlevie]

While a gummed up AFM vane can be a problem, the more likely cause of hesitation would be wear in the vane position sensor.

[nando]

i know youre having the same problem, i said i think you are exaggerating the severness, its an inherent problem of the flap style afm it takes say... half a second for the air to push open the flap and then the engine realizes it needs more fuel and then vroom. it can be worse if the flap is having trouble swinging, clean your afm better, dont just spray at it, maybe wd40 a little when your done cleaning it

i woulndt spray anything at the TPS as this is an electrical sensor and not really a mechanical peice

edit: and get a BENTLEY manual chilton is a POS

this isn't neccesarily true. you can get very good throttle response from an AFM, but most E30s have various vaccum leaks and non-working sensors that cause it to be bad. there is no "half second" lag on the throttle of my car, although when I first bought it there definitely was - turned out my throttle boot had several holes and cracks in it (that also caused a funny idle).

[skuyler]

this isn't neccesarily true. you can get very good throttle response from an AFM, but most E30s have various vaccum leaks and non-working sensors that cause it to be bad. there is no "half second" lag on the throttle of my car, although when I first bought it there definitely was - turned out my throttle boot had several holes and cracks in it (that also caused a funny idle).

heh, mine had that too...squeeled at high revs also