99 540i sligth misfire and rough idle??

I recently had some work done on my 540i done: water pump, valve cover gasket, new radiator, oil change, new performance exhaust muffler.

The muffler was the last to be installed and car was starting up fine until earlier this week. When I started the car cold the whole car will shake and the rpm's will rev slightly. As the car worms up the shaking lessens and ultimately stop, the slight rev(misfire) will happen for the first 2 minutes of driving when shifting into neutral to coast to stop. After about 2 minutes of driving and being warmed up it drives perfectly normal, I forgot to mention I have no warning lights on in dash too... This seemed like it started happening after the hurricane but the car couldn't have been effected because the car was parked on an incline with steady run off.

I was told by a reputable mechanic that it's like to me moisture build up in the exhaust and once car is fully warmed it evaporates the moistures hence is why car normal after warm up. This supposedly happened when new muffler was installed at meineke. But I can't be sure so does anyone have any suggestions???

Post some codes, miles on the car, and stick or auto.

If it's exhaust moisture, why does it keep happening?

there is 98k mi. on the car and it's a 6 speed manual I barely drive it, it sit's with a ca. It has been raining here for the past week well I should say hurricane, i'm 2 miles from Coney Island where everything is under water and all symptoms started after it hit. It has been been wet and moist the whole time and now its snowing. Car runs fine after it warms up and I drive it for .5 mile. What codes do you mean and how do I get them??

"What codes do you mean and how do I get them??" The car can report trouble codes by way of a scan tool. These codes can suggest where the problem lies.

I suspect that, from that question, you need to get the car to a BMW specialist, since it's probably beyond your diagnostic skills. Your "reputable mechanic" sounds like a moron to me.

I said I was told by a reputable mechanic this could be the problem based on what I told him over the phone. My mechanic never was able to run and diagnostics because he never had the car. I am supposed to bring car in when the weather improves in next few days and instead of paying a $100 for diagnoses fee where I know he will find the problem I gave this forum a shoot. I think I mentioned there are know service or warning lights on the dash, would there still be codes without the those lights?

I know I can take the car to AutoZone for a free Diagnostic test, I was actually thinking about buying one too. I guess that will be my next move if you can confirm I can still get a code reading with an eliminated warning lights..

The CEL lights up when there are emissions-related problems. Some codes will not light it. Also, some code readers will not access BMW-specific codes.

"it sit's with a ca" what's a "ca?"

My mistake I meant to type " it sit's with a car cover". Thanks for the helpful info. I will make sure I get a scanner that reads BMW codes. When I do find out what the code(s) are I will post them.

Vanos?
My car also idled very poorly and had fluctuating RPM when cold before I replaced my seals.

Roughly, How much is that going to run me?

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

Someone with a 540, help me out here...does your car have the vacuum actuated flaps that go to the muffler to open or close one or more of the exhaust ports? I think that was on later cars, not sure. If they do have these vacuum actuated muffler flaps, I'm wondering if the new muffler didn't have them and the vacuum line was left unplugged.

I don't think any e39 had anything like that, even the M5.

Is there any steam coming out of the exhaust when it's cold? If there is moisture in the exhaust you'd should see some steam.

How much of the exhaust was replaced? Did it start after the exhaust was changed or after the storm?

No steam coming of exhaust and it started after the hurricane. The day after hurricane u had to drive, that day it was fine. I parked and then a couple days later I went I drive it and when I started it the symptoms I mentioned above started happening. In going to get it scanned tonight or tomorrow to see if any codes come up and then after that look into the banks seals. That's what it seams like problem to me. I will post the codes when I get them, if any come up.

I'm at autozone right now and the scanner said there are ZERO code malfunctions. Guess that mean it's not a serious issue??? I think the next step is go to BMW service or BWW specialist?? The car drives perfect when it's warms up, no loss of power no hesitation. This is makeI g me crazy, I has a new radiator out in found that or thrown something off??

Because anything having to do with the vanos is going to be expensive and I def don't want to start getting into that if I don't have to and if it's not the problem.

it sounds like a vanos seals problem

I have a feeling it's the vano's too I will find out Monday. What causes the seals to go on the vano's system, or any vano's problem?

Unfortunately this seals are of very poor quality, BMW knows about this problem and they simply don't care. Google Bisan systems because that's the company that I use when I replace mine, I did mine about two years ago and I believe they cost me about 60.00 dollars good luck

My 740i had the same problem, 2 "cheap" things to check:

1) when the waterpump was changed did the thermostat get changed? These thermostats have a heating element that can fail causing the car to warm up slowly and misfire until warm (fuel maps are off and adjusted by the computer) If you did the waterpump yourself make sure you plugged the heating element back in, or even if it was a shop for that matter.... It is a small spring loaded connector on the passenger side of the waterpump.

2) Is your valve cover gasket leaking? Your spark plug wells would have some oil pooling around the spark plugs causing misfires.

My bet is your thermostat heating element has gone bad, or the thermostat itself is stuck in the open position (that is how they fail)

The thermastat was not changed!! But everything else seems to be plugged in, as for the Valve cover gasket ill have to have that checked out for me. I really hope it's one of these inexpensive problems.

Originally Posted by akillies

The thermastat was not changed!! But everything else seems to be plugged in, as for the Valve cover gasket ill have to have that checked out for me. I really hope it's one of these inexpensive problems.

Well I would bet my money on the thermostat.

So i have my car at the renowned Mihn's auto repair in brooklyn NY, they specialize in German vehicles. They have just informed me there is a bad exhaust manifold leak(gasket) and that is probably what's causing the rough idle and hunting RPM needle when cold. Can I get some feedback on this diagnoses, or if anyone disagrees and why? After they replace the gasket they will re smoke the system and check further for anything else.

I stand by my diagnosis, Autozone can't pull codes like the Thermostat heating element... I hope you get it sorted out.

Thanks.. I know autozone does have the complex BMW technology I need that's why I brought it to a specialist. I told the supervisor everything you suggested(rrtec) as well as possible vanos issue. frankly I hoped it was what u said rrtec. They have the latest BMW equipment so I trust their judgment. I will know tomorrow morning what's what. I think either way I had to fix that manifold gasket. Will post update in the morning.