Throttle Response Sluggish

[Vefu]

Hey guys.

I've been having a problem recently where while the car is running and it is still cold, after I shift gears and put my foot back on the accelerator there is about a 1 second delay from me pushing down and when you can feel the car start to accelerate. Another problem the car has that might be related is that sometimes when i'm slowing down, i'll put the car in neutral and the RPMs will drop to like 200~ then come back up, then the car will stall and die. After this happens I have to wait a minute or two to start it back up because if I try to start the car immediately it wont turn on.

So do you guys think these two problems are related? And what should I start looking at to fix?

[Sagaris]

It is likely that vacuum leaks are a big part of the problem. Search about vacuum leaks, there are many threads which show a complete list of items to check (mostly thanks to jlevie).

Also check the health of your ignition system. My hesitation was mostly caused by having a really worn distributor cap, rotor, original plug wires, and worn plugs.

There are so many things to check on the engine (including how dirty the injectors are, cam timing, o2 sensor, coolant temp sensor, fuel pressure etc) but fixing vacuum leaks and refreshing the ignition system are, in my opinion, the first steps.

[Kershaw]

when was the last time the valves were adjusted?

i'd definitely have the engine smoke tested (jlevie's favorite thing to do in the world) for vacuum leaks.

[jlevie]

Yes I recommend a smoke test frequently (too frequently in some folks opinion). But there is a reason for that. An engine with electronic fuel injection is extremely sensitive to intake leaks. You can try to find them visually or with carb cleaner (which only works sometimes and on some leaks). But a smoke test, properly conducted, will find any and all leaks and in places where you'd never think to check. There are other possibilities, but until intake leaks can be ruled out it is pointless to pursue those.

Have a shop run a smoke test and go from there.

[Sagaris]

And for the record, Kershaw's sig is not the proper procedure for a smoke test


sorry dude

[Vefu]

Thanks for all the help guys, I'll try and gather some money up to go get my car tested (poor college student). How much should I be looking to spend to get this done?

[Sagaris]

You can inspect the plugs, cap, and rotor and determine if they are in dire need of replacement (if cash is tight) but if a perfectly running BMW inline 6 is on your agenda then replacing those will be part of the equation.

The spark plug wires are tricky to diagnose. You can check the resistance of the wires, and pay attention to symptoms of bad wires (hesitation and bogging on rainy/humid days) but my experiences have shown that even testing those things isn't always a clear indication to whether it is beneficial to replace them or not. Having a perfectly running car is more important to me than how I spend money so for peace of mind I just went through and replaced everything in my car (such as plug wires etc.) just so I know that it is new.

Expect ~$100-125 for plug wires, check the classifieds to see if anyone is parting out a car or selling a lightly used set.

Cap and rotor, make sure you get matching brands for both cap and rotor to avoid fitment/gap issues. I think I remember the rotor being about $20 and the cap being closer to $50,

Spark plugs should be about $25-30 ( $4 to $5 a piece ) for NGK ZGR5A, which is my preference for the M20, gapped at 0.032"-0.035" (another personal preference)

I have never run a smoke test and do not know how much they cost. A friend was creative and made his own smoke tester which revealed two leaks.

[Vefu]

Well, I just went through the service history to check when everything you stated was last replaced.

Distributor Cap and Rotor - 25k miles ago
Spark Plugs and Spark Plug Wires - 22k miles ago

The maintenance schedule says that these should be replaced every 30k miles, so shouldn't those all still be good?

I also saw that the PO was having the same issues and got the car smoke tested 24k miles ago back in 2007. So I guess this car has been having these idle issues for a long time...

[Hey_You]

Did they use quality parts? I had a wire set from Bimmerworld crap out on me after 500 miles, they caused an arc at the spark plugs and at the coil. Had to replace the plugs (again), wires (again), and coil because of a crappy set of wires. I was in denial of the new parts being faulty, but it happens more than you think

[Vefu]

Did they use quality parts? I had a wire set from Bimmerworld crap out on me after 500 miles, they caused an arc at the spark plugs and at the coil. Had to replace the plugs (again), wires (again), and coil because of a crappy set of wires. I was in denial of the new parts being faulty, but it happens more than you think

Spark Plugs -Bosch WR9LS
Spark Plug Wires - 12121705714
Distributor Cap - Bosch 03195
Distributor Rotor - 12111734110

[Hey_You]

Have you tested your TPS sensor?

[Vefu]

No, I haven't tested anything yet. I just came home from school for Christmas break so now I have 6 weeks fix this problem before my 200 mile drive back down to school.