Shudder, hesitation on takeoff

[Titius Justus]

I'm experiencing what could be described as a misfire, a hesitation when pressing the accelerator from a stop. If the accelerator is pressed gently for a soft takeoff, the engine smoothly accelerates the car. If I press it quickly to request a slightly more aggressive takeoff (like pulling out into traffic) the engine hesitates. Once the engine reaches about 2,000 RPM, it pulls hard and smooth. The engine is very strong and the transmission does not slip. I don't seem to be experiencing any issues at an idle or above 2,000 RPM under hard acceleration.

It seems to be more noticeable when the engine is hot and when the a/c is running.

[affende]

Im interested in this as well. I have similar symptoms.

[nostness]

I had the same issue and it turned out to be a rather large tear on the bottom of my air intake boot. Once in a great while, I would get a whistle at idle but the hesitation only happened while pulling away from a stop. The hesitation and occasional whistle would only occur when the engine was warm, so I would start there.

[ross1]

A vacuum leak will cause such symptoms. A misadjusted throttle position sensor could also cause it.

[Titius Justus]

I'll check the intake boot. There are two ports just before the TB that come in from underneath; they are split but they seem to be holding the tubes in place. I didn't think much of it...

Why would it only do it when the engine is hot? Expansion/softening of the rubber when warm?

I did not know the TPS was adjustable; Is there a procedure in the Bentley's manual for this?

[Titius Justus]

I tried unplugging the O2 sensor. It did not help. It did turn on the check engine light...

[danielson]

I live worth the same issue everyday. I've checked a lot of things under the good but I think it's a VANOS issue.

[Titius Justus]

I changed out the intake air temperature sensor, the one which screws in from under the intake, and has a black tapered element about 3" long. No change. I also swapped the throttle position sensor. No change.

I replaced the engine a few months back and I kept all the sensors, throttle body, intake, etc. These are the parts I used to swap them out with.

Danielson, that's a new possibility I haven't considered. I didn't think the VANOS was actuated until around 2500 RPM... Wouldn't the computer pick up on the camshaft position and correct accordingly? I do have another VANOS actuator I believe...

[danielson]

I've read that VANOS works under 3k or so. It actually retards the timing at lower rpm for better torque and fuel consumption. That is why when the VANOS starts going out moist of the driveability issues are low rpm related.

I spent an evening reading tons of posts lol.

[Titius Justus]

Is it simply the actuator? I have another one I can swap it out with. Or is it the helical mechanism on the camshaft sprocket?

I have found that the problem is worse when the AC compressor is running/engaged.

[Ley3198]

I'll check the intake boot. There are two ports just before the TB that come in from underneath; they are split but they seem to be holding the tubes in place. I didn't think much of it...?

Believe it or not, this will cause your problem. While your at it, check the hoses at the ICV. Also, ICV can go faulty internally and cause a vacuum leak, smoke test it.

[Titius Justus]

I wrapped the split ports with gorilla tape and they are good and tight now.

What is a smoke test?

[danielson]

Do a quick Google search on bad VANOS symptoms. Its basically what our issue is. The seals in the VANOS unit wear out and it doesn't hold the pressure required to advance the camshaft timing, this is why we get the shudder and terrible low end power. Like I said, I have tried everything except clean out the intake idle control valve.

[Titius Justus]

I've noticed the symptoms are much worse when the AC compressor is running. With the AC off, and a fast but smooth pedal push, the car launches quite nicely from a stop. Trying to do this when the AC compressor is running, and it acts like there is a dead spot in the throttle.

[shogun]

What is a smoke test?
= google: smoke test engine vacuum leak or Smoke Leak Detector or vapor Leak Detection

[Binjammin]

I'd check the tranny fluid level just to be on the safe side.

[ahrensNW]

+ 1 on the intake issue. I had a massive hole on mine caused by my fan and it caused the same symptoms the op described

[Titius Justus]

I don't smoke and I don't have access to a smoke machine. What I did do was hooked up my shop vac to the intake hose, before the MAF, sealed it well with tape and put the vacuum unit in the trunk and turned it on. It's a powerful vacuum and it literally collapsed the intake hose under vacuum LOL...

I was unable to locate any leaks in hoses or gaskets using this method. I did observe some vacuum bleeding through the IAC though. I removed the I take boot from the TB and plugged it to isolate it to check for leaks, this is when I noticed vacuum in the intake. The o ly connection I could find was the IAC. Is this normal, or should it be completely shut when the car is off?

At this point, since I can't find any leaks, I'm thinking about getting all new gaskets and hoses, then removing the intake. I'll then carefully examine everything, clean the IAC, etc and reassemble.

[Titius Justus]

I was at Advance Auto Parts today to get a replacement Denso Iridium Power (5304) spark plug for the one that had the porcelain isolator come loose inside the base, causing misfire and combustion leakage (and what I thought was one hell of a lifter tapping). It occurred to me that the plugs are pre-gapped and I put them in straight out of the box, as they had a nice sleeve protector over the threads which protects the electrode and ground from impacts. They say on the package that "In most cases, gapping is not necessary". The gap is preset for 0.044". The factory spec is 0.032". Do you think this could cause a problem?

[danielson]

nope, im telling you man its the the VANOS seals. what you are describing is the exactly what a worn VANOS seals causes. low end power, hesitation, lower fuel economy and drive-ability issues. To test if the solenoid is working or if the VANOS holds pressure. 1) disconnect solenoid plug 2.) connect two wires, one to + and the other to - ( BE VERY CAREFUL AND WATCH THE POLARITY...solenoid plug is stamped with a + and -. 3.) ground out the - and connect the + to a 12v source 4.) at idle the car should lower in rpms if the VANOS is working fine, if it does nothing then your VANOS is toast. Either the solenoid is bad or the seals are gone. The solenoid rarely fails.

video here

http://youtu.be/d7_mAceNhg0


good read.

What are the symptoms of a failing vanos?
Overall loss of torque and power, particularly in the lower RPM range, < 3k. Bogging then surging at 3k RPM. Uneven power distribution and RPM transition. Engine hesitations in the lower RPM range, < 3k. Louder idle and intermittent idle RPM hiccups. Difficult takeoffs. Loss of power and bogging when AC on. Increased fuel consumption.
Double vanos cars with the M52TU engine (98/99-00) experience cold weather cold start idle jolts and possible stall.


more here.

http://www.beisansystems.com/faq.html

[hellwagon]

My m20 (without vanos, obv) does the same thing.

[danielson]

My m20 (without vanos, obv) does the same thing.

You may have a vacuum leak or the AFM needs adjusting.

[hellwagon]

You may have a vacuum leak or the AFM needs adjusting.

Turns out my coolant temp sensor was bad. After putting a new one in, my 525i runs much better with no stuttering or hesitation.

[sbeckman7]

Turns out my coolant temp sensor was bad. After putting a new one in, my 525i runs much better with no stuttering or hesitation.

?!?

[E38740iMD]

on m20 cars the cts can cause weird stuff to happen...also in m30s too

[hellwagon]

It also cleared up my hard start issue. Cts = miracle m20 sensor. Lol

[Ley3198]

OP - After you fix your vanos, try copper plugs.

Platinum and iridium plugs are usually better suited for newer cars.

[Titius Justus]

OP - After you fix your vanos...

Here is the link to YouTube where I uploaded the video I took of the VANOS test on my engine:

https://www.youtube.com/watch?v=LreEdNYx7VY (http://youtu.be/LreEdNYx7VYSo)

So. What do you think? Is my VANOS bad?

[ricks5series]

I'm experiencing what could be described as a misfire, a hesitation when pressing the accelerator from a stop. If the accelerator is pressed gently for a soft takeoff, the engine smoothly accelerates the car. If I press it quickly to request a slightly more aggressive takeoff (like pulling out into traffic) the engine hesitates. Once the engine reaches about 2,000 RPM, it pulls hard and smooth. The engine is very strong and the transmission does not slip. I don't seem to be experiencing any issues at an idle or above 2,000 RPM under hard acceleration.

It seems to be more noticeable when the engine is hot and when the a/c is running.

I'm having the same issue with hesitation when the car gets hot, did you ever resolve your issue and if so what it was it?