To Do or Not To Do?

[Will308]

I'm at a crossroad with my 91 525i. I've been chasing a rough idle/ miss problem for a while now and so far no-one has been able to diagnose the source.
I have it at the shop currently. ( not the shop I normally used) to check it out. I felt a fresh set of eyes and ears might help. They went through the ignition system( coil packs, boots, plugs) and the injection/intake systems and came up with nothing. Everything is working properly.
The tech is recommending a freshening up of the head. Remove it, machine it, change the valve seals, clean and lap the valves, new head gasket, etc.
He's telling me the cost to do this would be approx. $ 1600.00. He's 95% sure this would cure the problem, but not 100% sure. He thinks the valves may have some carbon buildup causing them to not fully seat.
Right now the car does burn some oil, about 1 quart every 2000 miles. But I don't have any white smoke comming out of the exhaust system or oil in the coolant. No real problems other than the idle. It's more of an annoyance than anything.

My question. Given the value of the car and the cost of the repairs do I just drive it until it really needs the head work, or pony up the money for the repairs hoping it corrects the problem?

Thanks in advance!

[tim s]

there is several sensors, crank, cam, throttle position, air flow meter, temperature. you need to thoroughly test their resistence & see if it meets spec. it could also be vaccuum leak, what is the compression test results? i just spent $800.00 on my 540i/a trying to find why it has a slight mis & runs rough up to 1300rpm's & smooths out around 2000rpm's. mech. is now telling me he thinks it is the torque convertor, but the dealer says the idle is almost perfect.
tim s.

[Will308]

there is several sensors, crank, cam, throttle position, air flow meter, temperature. you need to thoroughly test their resistence & see if it meets spec. it could also be vaccuum leak, what is the compression test results? i just spent $800.00 on my 540i/a trying to find why it has a slight mis & runs rough up to 1300rpm's & smooths out around 2000rpm's. mech. is now telling me he thinks it is the torque convertor, but the dealer says the idle is almost perfect.
tim s.

I don't know what the results of the comp test will reveal. Tech thinks the valves are coated with carbon buildup or some other problem in the head. I though I read somewhere you could use crushed walnut shells to remove carbon buildup while the engine is running, and that it won't hurt the motor?

I'm more inclined to think like you, I think it's a sensor that's not funtioning properly. The rough idle is somewhat erratic. Sometimes it's worse sometimes better. I'm not sure I want to open up the motor ( at a cost of $ 1600.00) only to find it wasn't the valves in the first place.

As far as your problem is concerned how do they equate your problem with the converter?

[tim s]

they get extremly dirty & stop working properly.
get the compression test done. you can do it yourself. the tools are not expensive & it is easy to do.

as for my car they think the torque converter is out of balance. i did read that the valve body can fail in a way that the reverse has pressure continually even in neutral.
thanks
tim s.

[Bill R.]

this somewhere they had it all wrong. When carbon buildup on the backside of the intake valves first became a problem back in the 1980's bmw came up with a machine to remove this carbon, it was similar to a sand blaster but used walnut hulls instead of sand or glass bead.. walnut hulls won't remove aluminum like sand will...This process required removing the intake manifold and then this blaster would go up against the port in the head. You had to make sure that each cylinder had its valves closed and then you blasted the backside of the valve stem with the hulls to remove the carbon. Then you vacumed out the remaining hulls and carbon and went to the next cylinder port and did the same.... Nowdays there are enough intake valve cleaning chemicals like techron that the hulls are not longer needed. If your valves actually have enough buildup on them to prevent them from seating correctly then a compression test will show this. I doubt that this is the problem. I would try another mechanic myself.

I'm at a crossroad with my 91 525i. I've been chasing a rough idle/ miss problem for a while now and so far no-one has been able to diagnose the source.
I have it at the shop currently. ( not the shop I normally used) to check it out. I felt a fresh set of eyes and ears might help. They went through the ignition system( coil packs, boots, plugs) and the injection/intake systems and came up with nothing. Everything is working properly.
The tech is recommending a freshening up of the head. Remove it, machine it, change the valve seals, clean and lap the valves, new head gasket, etc.
He's telling me the cost to do this would be approx. $ 1600.00. He's 95% sure this would cure the problem, but not 100% sure. He thinks the valves may have some carbon buildup causing them to not fully seat.
Right now the car does burn some oil, about 1 quart every 2000 miles. But I don't have any white smoke comming out of the exhaust system or oil in the coolant. No real problems other than the idle. It's more of an annoyance than anything.

My question. Given the value of the car and the cost of the repairs do I just drive it until it really needs the head work, or pony up the money for the repairs hoping it corrects the problem?

Thanks in advance!

[winfred]

the walnut shell thing is like sand blasting, they remove the intake and rotate the motor till the valves are closed on a given cylinder and blast away, being soft if any are left behind they don't hurt anything,

I though I read somewhere you could use crushed walnut shells to remove carbon buildup while the engine is running, and that it won't hurt the motor?

[Bill R.]

difference.









[





QUOTE=Will308]I'm at a crossroad with my 91 525i. I've been chasing a rough idle/ miss problem for a while now and so far no-one has been able to diagnose the source.
I have it at the shop currently. ( not the shop I normally used) to check it out. I felt a fresh set of eyes and ears might help. They went through the ignition system( coil packs, boots, plugs) and the injection/intake systems and came up with nothing. Everything is working properly.
The tech is recommending a freshening up of the head. Remove it, machine it, change the valve seals, clean and lap the valves, new head gasket, etc.
He's telling me the cost to do this would be approx. $ 1600.00. He's 95% sure this would cure the problem, but not 100% sure. He thinks the valves may have some carbon buildup causing them to not fully seat.
Right now the car does burn some oil, about 1 quart every 2000 miles. But I don't have any white smoke comming out of the exhaust system or oil in the coolant. No real problems other than the idle. It's more of an annoyance than anything.

My question. Given the value of the car and the cost of the repairs do I just drive it until it really needs the head work, or pony up the money for the repairs hoping it corrects the problem?

Thanks in advance![/QUOTE]

[ocampg]

I had the same problems on my 89 525i, it got to the point that the car was stumbling/missing so bad that the car would not drive. Anyway, it turned out to be the MAF sensor, purchase a new/rebuilt one from autozone, its only $100 plus $50 core charge. I bought a used one from someone on this board, and it also was defective. I still have a rough idle, which i believe may be the ICV, but changing the MAF sensor definitely solved my engine stumble/misfire problem.

[MicahO]

That's how they clean motors on T37 trainers.....

Of course, on those motors, they come shooting out the backside

[Will308]

they get extremly dirty & stop working properly.
get the compression test done. you can do it yourself. the tools are not expensive & it is easy to do.

as for my car they think the torque converter is out of balance. i did read that the valve body can fail in a way that the reverse has pressure continually even in neutral.
thanks
tim s.

Replaced the idle control valve myself ,along with the modified rubber pipe that connects it to the intake manifold, a while ago. No improvement.
Thanks for the reply!