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Steve
Steve, BMW Expert
Category: BMW
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BMW 318i SE Aug 1994; M40/43 Hi, My ancient BMW has started

Resolved Question:

BMW 318i SE Aug 1994; M40/43
Hi,
My ancient BMW has started idling at an indicated 1500 RPM when cold and, (gently) hunts between 1400 & 1800 when warm. Disconnecting the throttle position sensor does not affect anything.
The head was recently done so I am presuming its not a air leak between engine and throttle.
Where do I start, to get the idle back down to the advertised 800RPM?
SA
Submitted: 2 years ago.
Category: BMW
Expert:  Steve replied 2 years ago.
Did this start immediately after the head job?
Customer: replied 2 years ago.

Hmm, no. It started 2-3 weeks later!

Also, at around that time (almost a year ago now) I recall a strange one off while town driving, when all the instruments on the cluster, instantaniously, shot up full scale for a few seconds and then all resumed normal. At the time I assumed the overshoot had machanicaly damaged and offset the rev counter but I am more and more convinced the engine is now actually running faster. Is there any way to get a RPM reading?

It passed its MOT last month so the mixtures must be more or less OK; I'm a Domestic gas engineer with a gas analyser (if I knew what numbers I was looking for). Is there an electronic regulator in the cluster?

Sorry to OD on detail.

SA

Expert:  Steve replied 2 years ago.
What is the last 7 digits of the vin?
Customer: replied 2 years ago.

Last seven digits: "KB05141". SA

Expert:  Steve replied 2 years ago.

Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you

only the rpm guage gives an rpm reading on this model. you could possibly install an aftermarket tach if you wanted

despite the recent work I would still check for air leaks first

I would also test fuel pressure and replace the fuel filter.

additioinally I would clean or replace the idle valve, airflow sensor, throttle body and crankcase vent valve

Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.

Customer: replied 2 years ago.

Ok,I've got where you are going; thanks for the suggestion of an aftermarket Tacho.

Is there any other way other than simply eyeballing/squeezing the pipes when looking for an air leak, to gauge for leaks?

Similarly Fuel Pressure? There does seem to be plenty of fuel pissing about when I had the fuel rail off and failed to refit properly first time.

Ta SA.

Expert:  Steve replied 2 years ago.

Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you.

.

the proper test for an air leak is a smoke test with a smoke machine

if you do not wish to invest in such a test, the simpler way is to use a can of carb cleaner and spray around the intake while the engine is running - if the idle changes you know carb cleaner is getting into the enging and a leak is present.

fuel pressure needs to be tested wiith a pressure guage.

Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.

Steve, BMW Expert
Category: BMW
Satisfied Customers: 23216
Experience: BMW Expert
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