Is this hesitation normal (includes video)?

[Earendil]

Video says it all I think.

http://www.youtube.com/watch?v=UvcjCjlysAQ

Is this normal? Car is incredibly strong and smooth across the entire RPM range, idles what I believe to be like any M20, and causes no complaints otherwise. My father has an iX with the same issue but worse. His actually effects his ability to start on a steep slope. Mine will just cause a slight bucking when transitioning from closed throttle to open.

I've checked many things already. Of note I've checked the TPS a half dozen times and it's solid and in the correct position. Thoughts? Maybe it's normal?

[Sagaris]

I had the same issue as well.

I had a few small vacuum leaks which didn't affect the idle or driving performance at all, but that initial throttle tip-in would hesitate like yours.

Vac leak #1 was the breather tube from the valve cover to the throttle body being split where it connected to the valve cover.

Vac leak #2 was due to a loose nut on the intake manifold.

I also replaced the AFM with a rebuilt unit. All three of those things equally improved the off-idle hesitation.

All is well now

[hadeye_bm335i]

i have the same prbleme . yea i thing its vacum leaks

[blocke]

Mine did that pretty bad when I had the AFM, to the point that it made it unbearable to drive. Much improved once I got my miller MAF conversion. Still slightly there, so I'm assuming there is a leak somewhere, but its nowhere near as bad as it was.

[Cabriolet]

mine does the same thing and its pretty bad so much so that it will stall from doing that.

[nando]

a very slight delay is normal (and not cause by the AFM, either). A big delay, bucking, stalling, etc. is not normal and is most likely caused by a vac leak, but there's a ton of other things that could also do it.

[Earendil]

a very slight delay is normal (and not cause by the AFM, either). A big delay, bucking, stalling, etc. is not normal and is most likely caused by a vac leak, but there's a ton of other things that could also do it.

And that is what is bothering me. The engine got a new head gasket and valve springs last year, which involved lots of cleaning and new seals. That engine is as tight as can be. The only place a vacuum leak could occur would be on the hoses leading to the brake booster. Unless the charcoal line can leak?

I do have a spare AFM. Thanks to a PM from Rynn I was reminded of the Porsche AFM rebuilt procedure. I dismantled the spare and drug out the multimeter. Spiffied the thing right up and swapped it for the one that was in there. The car fired right up, so I took the original one and cleaned it up as well. It seemed to have a flat spot at idle, so I moved the track a little and it regained some of that.

Turns out the first one I cleaned, the spare, had major issues up top. It's going to need some more work. After swapping back in the original everything went back to normal. No noticeable difference in that slight initial hesitation.

Perhaps I'll see about replacing the lines to the brake booster to see if that does anything. I attempted to clamp off the lines once, to see if the booster its self was the one leaking, but that had no effect.

It was the state of my engine and my inability to do anything to negate the hesitation that caused me to ask the question. So far it seems like a few people see a similar thing... but it wouldn't be beyond belief to think that we all have small vacuum leaks :)

Maybe The next time I'm around a bunch of E30's I'll ask to play with everyone's throttle :shock:

[Sagaris]

Maybe The next time I'm around a bunch of E30's I'll ask to play with everyone's throttle :shock:

Be certain that you are fitting latex inspection gloves over your hands with a very serious look on your face while asking them.

[davem]

it wouldn't be beyond belief to think that we all have small vacuum leaks :)

this

I had a vacuum leak at the intake manifold gasket found via smoke test, it caused check engine lights whenever the throttle closed, very rough idle etc. resealed it up, and no more CEL at idle and it runs better... BUT when it's cold it still has a hesitation and i've noticed if i'm coasting down a hill in fifth, CEL comes on until i blip the throttle...

I think it's the brake booster hose, those vacuum hose elbows at the throttle body, injector seals (they still leak a bitafter new ones and being oiled). It's fucking annoying because my m20 is a lot cleaner than most.

[SpecM]

a very slight delay is normal (and not cause by the AFM, either)

what is it caused by?

[riceh8r]

not sure of this answer, but an older bimmer mechanic told me this just today. i did the same throttle test by hand for him...he said "you don't have a cat on your exhaust, do you ?" he says that small amount of back pressure missing causes that. hmmmm. i don't know. quick poll: how many of you are running without a cat ? i wanna know, so i can evaluate his diagnosis.

[Sagaris]

My guess is that the AFM just isn't the best at providing accurate load/airflow measurements during sudden transient conditions like that. The flap can peg open when you just give it a quick blip and the timing+fueling just wont be optimal. .. aside from the whole engines natural response time.

[dandrewg]

My car suffers from this problem as well, and I am running an exhaust with no catalytic converter. I have noticed that sometimes when the engine is cold (first start up of the day) this problem is absent, which leads me to believe that it's not an engine response time issue. My engine coolant temp. sensor is new. Thoughts?

[Sagaris]

My first thought would be the oxygen sensor because the oxygen sensor does not provide feedback to the ECU when the engine is cold (open loop). Once the engine is warmed up and running in closed loop, it listens to the oxygen sensor for feedback. If the oxygen sensor is old or damaged then the ECU will not be fueling the engine properly.

[nando]

actually, it does. it only takes a few seconds for the O2 sensor to heat up, and once it does it immediately provides feedback and goes into closed loop mode.