Rough Idle, Runs Rich, Overheats a little

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Joined: Thu 08 Apr, 2021 04:00
Posts: 1

  Z3 roadster 1.9

Rough Idle, Runs Rich, Overheats a little

Post by chauncey »

I have a 1997 BMW Z3 1.9L M44
I’ve had it since Jan. 2 2021
It’s mostly been in and out of the shop since has had plenty of parts replaced listed below:
Upper/Lower Rad Hoses
Rad Cap
Fan Clutch
Front and Rear coolant piping
Auxiliary Fan Fuse
Blower Motor Fuse
New stock ECU
Valve Cover Gasket
Spark Plugs
When I first got it, it would overheat since the previous owner had it sat for about 2-3 years, after all this done to the Z it doesn’t overheat as fast although it still does slowly, I can drive about a mile until it reaches red and it also runs very rich and has a rough idle, my first thoughts are the ignition coil and maybe the fuel system needs a good look through, possibly an o2 sensor, I also think that maybe I need a new auxiliary fan to keep things cool idk, I’d like to narrow things down to see if I can diy a few things before taking to my mechanic

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Joined: Sat 05 May, 2012 22:46
Posts: 684

  Z3 roadster 1.8 TU
Location: Newport South Wales UK

Re: Rough Idle, Runs Rich, Overheats a little

Post by colb »

Rough idle on M44 known issue but if its bad and fuel trims are high this is usually down to holed or split rubbers after the Maf check out the inlet hoses to the throttle body and all vaccum lines across the engine for splits. A smoke test will reveal any you can't find visually. Disconnect the Maf electrical plug and see if running improves as disconnected it will run on default settings. If it runs better then suspect the Maf but check for air leaks first. AS to cooling I note you changed the thermostat, no mention of a new waterpump, that may be an issue, not that expensive to change. Exhaust sensors should be considered after you confirm you have no air leaks. If you have diagnostics that can view live data then take a look at the exhaust sensors, the pre cat sensors should be producing a nice regular wave form as their voltages range up and down, if they are not then suspect them.
1999 BMW 1.8 Z3
2003 BMW 2.5 Z4
1998 Honda Deauville NT650V

Mike Fishwick
Joined: Fri 19 Jun, 2009 10:27
Posts: 2063

  Z3 roadster 2.8
Location: Daglan, France

Re: Rough Idle, Runs Rich, Overheats a little

Post by Mike Fishwick »

An inlet air leak usually causes the EML lamp to come on, and a fault code indicating 'Lambda Voltage Implausable' due to the associated weak mixture.

You do not tell us why you feel the engine is running rich - a rough idle can just as easily be caused by overheated spark plugs, the high coolant temperature telling us that this is a basic problem.

I agree that the water pump is an obvious thing to suspect, as the type with a plastic impeller is known to have a problem - the impeller coming loose on the shaft when the engine warms up, and therefore reducing flow. The symptoms become worse as the engine warms up and the coolant temperature increases, which makes the slippage worse.

Why did you need a new ECU? Problems here are very unusual - or was it a desperate hope?

The M44 is claimed to suffer from cylinder had warping, which will promote loss of collant and high temperatures, but this would be obvious.
A Z3 is not just for Christmas - it's for life!

Joined: Fri 08 May, 2015 19:09
Posts: 26

  Z3 roadster 1.9

Re: Rough Idle, Runs Rich, Overheats a little

Post by Benw123 »

Having recently changed my water pump, I agree with the other posts that it's worth looking at. My 1999 M44 engine's original pump had a folded metal impellor (not plastic, even though I believe it was the original), but at 96,000 miles, there was a lot of play in the bearings. The new Mehle pump I fitted had a slightly different cast-metal design.

And with the MAF, mine also went awry last year. There was no EML, but there was a fault code. It was obvious something was up because the engine idled continuously at 1,000rpm. I disconnected it for a few weeks until purchasing a used replacement. Not only did this solve the problem, but strangely the engine idles much more smoothly than it did before.
99/T Z3 1.9 twin-cam, Boston Green, black leather

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