[billgti]

with the car in drive (e.g. stopped at a traffic light) and with the AC on, the idle surges by a couple hundred rpm and the car shakes very noticeabley. happens every 5-10 seconds or so. gets worse with the AC cranked up to max. doesn't happen when the AC is off.

what's going on here? Idle control valve? give me some ideas guys. thanks.

[persian54]

if you find out... let me know...

[billgti]

any ideas?

[sbux]

emission control failure ?

[ragingclue]

Yeah if you find out, let me know too.

[mtkid]

I also have this problem

[hotnikks]

Damn alot of people have this and no one knows... I may be experiencing this also not sure. Subscribed

[Potty_Pants]

ac compressor restrictions... ?

could the compressor be failing and providing abnormal restrictrion on the belts ?


ppp

[ragingclue]

I know there should be a normal slightly noticeable change when the compressor clutch is engaging/disengaging, or is that only on older cars? Anyway, the fluctuations are too close together to be this, as the duration of that cycle should be pretty long. Overall, I'm just not too impressed with the time it takes to get up to temp (or down to temp), or its effectiveness.

[billgti]

i know the ac compressor adds extra load and can therefore cause slight vibrations but what happens with my car is that there's a sharp jolt every 10 seconds or so...so much so that it actually jolts the car forward if i don't have my foot firmly on the brake pedal.

[ak335]

Happens to me too

[billgti]

Originally Posted by Potty_Pants

ac compressor restrictions... ?

could the compressor be failing and providing abnormal restrictrion on the belts ?


ppp

the compressor itself should be fine since the ac blows cold still. maybe something is wrong with how the ac clutch engages or idle air control valve?

[bsamoul]

It seems to me that with the AC on, it will inevitably make your RPM go up because the alternator has to supply enough power to it, and when your RPM goes up, you will start to move, just like when you hit the gas. So I believe that it is completely normal for that to happen.

[ragingclue]

Originally Posted by billgti

i know the ac compressor adds extra load and can therefore cause slight vibrations but what happens with my car is that there's a sharp jolt every 10 seconds or so...so much so that it actually jolts the car forward if i don't have my foot firmly on the brake pedal.

You would think that would more likely be related to the transmission. Odd. Maybe your compressor is running incredibly inefficiently and your engine has to overcompensate?

[clairvoyant]

check for vacuum leaks first ... clean the MAF, and IAC valve, check/replace airfilter....

as said before, it COULD be the beginnings of VANOS seals failure ... you can unplug the intake side vanos solenoid and if the problem stops, then that is likely your cause...

do you have any cold startup idle issues?

Originally Posted by billgti

with the car in drive (e.g. stopped at a traffic light) and with the AC on, the idle surges by a couple hundred rpm and the car shakes very noticeabley. happens every 5-10 seconds or so. gets worse with the AC cranked up to max. doesn't happen when the AC is off.

what's going on here? Idle control valve? give me some ideas guys. thanks.

[Wires]

I believe it's normal. At idle, they lean out the engine for maximum efficiency. During that time, power output is lower, and the engine is less forgiving to changes in engine load (aka A/C compressor suddenly snapping on).

My GM vehicles do the same.

[phxducwi]

I have the exact issue as billgti. it also improves a little with the a/c off but this is not just the slight change when the compressor kicks on, its more like a classic car with cams. a little bit of a shake...
I wish i knew because my car is out of warranty so i am trying to avoid the stealer. The vibration goes away as soon as your foot is on the gas.

hopefully someone will chime in that has gone through this before.

[Wires]

This is normal. In the "olden days" of like the '80's The car idled a lot higher (1300-1500RPM). With the closed loop EFI, it's now in that 500-700 RPM range. My GMC truck stutters when idling as well, and so does my BMW.....

[sofaonasock]

Originally Posted by billgti

with the car in drive (e.g. stopped at a traffic light) and with the AC on, the idle surges by a couple hundred rpm and the car shakes very noticeabley. happens every 5-10 seconds or so. gets worse with the AC cranked up to max. doesn't happen when the AC is off.

what's going on here? Idle control valve? give me some ideas guys. thanks.

+1

[billgti]

Originally Posted by clairvoyant

check for vacuum leaks first ... clean the MAF, and IAC valve, check/replace airfilter....

as said before, it COULD be the beginnings of VANOS seals failure ... you can unplug the intake side vanos solenoid and if the problem stops, then that is likely your cause...

do you have any cold startup idle issues?

thanks for your insight.

no cold startup issues. with the ac off, the idle is rock solid at around 600 rpm. with the ac on (and it gets worse with the fan speed turned higher, i.e. worse at with max a/c) the car occassionally jolts and i can see the rpms bounce up by a couple hundred rpm when idling at a traffic light.

i understand that it's normal to feel a slight vibration and see a slightly higher rpm with the AC on, but what i'm experiencing is a very obvious shake that occurs intermittently.

[ragingclue]

I'm getting unusual fluctuation of blower speed while it's on. It'll stop pushing air momentarily.

[billgti]

just in case any of u were still looking for a solution to this...

i took my car to a local bmw shop this week and the tech found the spark plugs to be in bad condition so i had all six of them replaced. the jolt at idle is completely gone at both stop lights with or without AC. so for anyone experiencing similar symptoms (my car had about 58k miles when it started to do this), check your spark plugs.