535 Idle issue continued

[wjbell]

Ok, so today I pulled my ICV on my 90 535i and it was pretty dirty. It had a coat of black residue. I used brake cleaner and thoroughly cleaned it. Reinstalled and no change. I also pulled the boot in between the air box and AFM and checked that out. It was very clean and the door operated smoothly. But with these two latest thing my car still has a rough idle.

The idle is not constantly rough, it's like a random minor miss. It idles smooth and then the idle will drop for a fraction of a second, then resume. I don't know if this is what they call the "lumpy idle". If you have the door open you can see the random miss in the engine and corresponding shake in the door. It's real slight but it's like the idle "drops out" then resumes.

So some history on the car... I bought the car from the second owner with 143K. Both owners took excellent care of the car. It turns out that when I bought it it needed the infamous big six head gasket job. When I got that done the shop said the engine was in excellent condition talking about the valve train, pistons, etc. They said it had been well taken care of. Compression was very close across all cylinders. So it hadn't been abused.

Since I've had the car I've had the head gasket changed, the valves have just been adjusted, the plugs are stock and gapped to .032 (heard the wider gap helps with idle), ICV and AFM are clean, air filter new, no vacuum leaks and new O2 sensor. The only thing I can think of is my injectors need a good cleaning or replacement. The shop where I take my car swears by something called the BG fuel service where they run some industrial strength cleaner through the fuel system for a couple of hours and it's suppose to clean the injectors, valves, etc.

Can anyone think of anything else I can try for a rough idle?

I know the big sixes aren't going to idle like a Honda but I don't think they should have a noticeable hesitation in the idle that feels like a miss.

Any help is appreciated.

[Jeff N.]

Try checking these things:

- distributor cap for corrosion + rotor
- plug wires; old or varies in resistance
- all the vacuum lines, in particular the 3mm lines under the intake manifold
- the hose that runs from the ICV to the intake manifold - cracks + tight hose clamp.
- intake boots after the AFM for cracks, tight hose clamps, tight connections with the fittings
- wipe off the back of your throttle plate with carb clean (never have figured out why this helps)
- Check the vacuum line from the intake manifold to the brake booster - the hose, the check valve (can crack and leak) and the fitting into the booster.
- Check the blue engine temp sensor connection for corrosion, clean if needed
- Check your injector seals, replace if needed
- While at it, stuff in some newer Ford Bosch 19 lb injectors
- Adjust your idle mixture on the base of your AFM

Yup. One of those for sure. That pretty much ought to cover it. Have fun.

[wjbell]

Try checking these things:

- distributor cap for corrosion + rotor
- plug wires; old or varies in resistance
- all the vacuum lines, in particular the 3mm lines under the intake manifold
- the hose that runs from the ICV to the intake manifold - cracks + tight hose clamp.
- intake boots after the AFM for cracks, tight hose clamps, tight connections with the fittings
- wipe off the back of your throttle plate with carb clean (never have figured out why this helps)
- Check the vacuum line from the intake manifold to the brake booster - the hose, the check valve (can crack and leak) and the fitting into the booster.
- Check the blue engine temp sensor connection for corrosion, clean if needed
- Check your injector seals, replace if needed
- While at it, stuff in some newer Ford Bosch 19 lb injectors
- Adjust your idle mixture on the base of your AFM

Yup. One of those for sure. That pretty much ought to cover it. Have fun.

Thanks!

A couple of questions... why the 19lb injectors? Will they effect MPG, power?

How do you know how to adjust the idle mixture on the AFM and where is the adjustment?

Those are probably the last things to check, but just curious.

[JMI]

You might want to consider this.
Check this thread. It solved a problem just like yours.

Jim