E30 318i M40b18: High / erratic idle issues NOW FIXED, stable at 800rpm + good throttle-response finally

After my cutting out when cold problem and no low-end throttle response from a busted lower inlet-manifold gasket (THIS POST) and high / pulsing idle issue from a poorly set throttle-stop screw (THIS POST), I have finally got the old E30 ticking over properly. It now sits at about 800rpm on idle and throttle response is smooth across the range. Pleasant.

E30 318i [M40]: Massive air leak SOLVED - lower inlet-manifold gasket

I had checked and re-checked the idle control valve [ICV], the air-flow meter [AFM], ignition system, tested for the fuel pressure, performed tests on the DME [ECU] to make sure that was working and even laboriously tested the wiring loom for continuity, but still the engine idles terribly when cold. It ticks over lumpy, shakes the engine side to side and cuts out at will, even when power is applied. 

I checked the timing and all was good, under the rocker-cover showed no defective valves and the cam-shaft doesn't look all that worn. I guess the only thing left to check is the injectors... right?? Now hold on a minute I hear the E30 and M40 engine gurus cry, the symptoms you've described point towards an obvious massive air leak in the induction system! 

This is true and is also the very first thing I looked for and tested. Initially I performed the 'spray' test using a can of brake-cleaner (though 'Easy-start', carb-cleaner or electrical-cleaner work too, anything with alcohol content). This involves running the engine and spraying brake-cleaner around the intake-manifold, ICV, vacuum hoses, throttle-body etc. If unwanted air is being sucked in, say through a split hose, the brake-cleaner will be sucked in and combusted by the engine causing it to rev higher. If you are spraying in one particular place and the engine revs increase accordingly then you have found your air-leak. Thing is, I did this test over and over again and it showed nothing. 

I’ve heard that air can be sucked in past the injector bodies when the rubber sealing rings have degraded over time and that the lower intake-manifold is also a main culprit, but spraying round this area made no difference to the engine revs or affected the poor idle. I did a compression test and the readings were a bit low, but not enough to cause any issues.

At this point I decided it to bite the bullet and begin stripping things down. The removal of the lower intake-manifold is quite complicated because it involves removing the fuel-lines from the rail, which is why I put it off, but clearly if you want to fix something then you need to get your hands dirty so off came the fuel lines and away came the lower manifold to reveal.... well, as you can see from the photo, a virtually non existent gasket. Sigh. 

Cylinder 1 has a massive gap where the gasket is no longer there, so whenever there is a vacuum in the plenum it’s just filling up with fresh air even with the throttle-body shut and this explains why the ICV appears to be doing nothing and leads people to look there first. Whoever was refitting the manifold was obviously in a rush because the broken gasket has folded over on itself, causing the air gap to be even bigger. I guess they just tightened it hoping to make a seal, but alas no. Cylinder 2 is not much better with a noticeable gap and the rest of the gasket squashed flat. Cylinders 3 and 4 are better, but still paper thin. It looks like this may be the original gasket and the past 35 years have not been kind to it (or to me for that matter).

So... looks like I have found the culprit of the rough idle. Finally! New gasket is ordered, a snip at £6.88! Amazing how such a simple thing can cause such a severe problem and goes to show how sensitive these ‘analog’ ‘80s cars are to air metering issues!

E46: New secondary air-pump - one last bash...

Thought I would have one ultimate stab at the E46 as it is such a nice car to drive and only let down by shabby bodywork, which I can do something about, and the super low idling problem, which apparently I can't.

I refitted the Vanos-actuator and checked for anything I'd disturbed under the inlet manifold, finding a loose wire connector which I clicked back in, though the CCV was all plumbed up fine. A replacement secondary air-pump and its hose / filter was £30 and the only thing now missing from the inlet arrangement. It took no time to fit, just two 13mm bolts holding it on and swapping the hoses over, but has still, alas, made no difference.

I've spent nearly £300 on parts to cure this engine of its fault, but nothing has done the trick so I guess I will have to call it a day and scrap her after all. Again a shame, as it has 9 months MOT and 4 months tax left on it. The running gear is sound, I sorted the brakes and the engine runs fine when underway, pulling well in all gears over 1500rpm. Handling is as sweet as any E46. The interior and exterior are in terrible nick, but thats nothing that couldn't be sorted with a day or two spent on it. That's only worth doing if the car is useable however, and it sadly isn't.

On top of the impossible low-idling, the handbrake-shoes have collapsed in some way and stick on completely in reverse with the handbrake off. This is probably from being used so much to stop the car while my right foot was still keeping the revs up, but is extra work regardless. A large M12 bolt holding one of the front shock-absorber struts broke while I was attempting to fit the coilovers months ago. I've been driving on it and the strut hasn't moved at all, but it too will need replacing at some point and removing the stud will be interesting. Inside the car, the fan for the heater/blower doesn't work and the driver's door card is missing, meaning no speaker or door handle. Exiting the car with dignity can only be done by lowering the window and reaching out for the other handle, but all these foibles I rather liked. Using it every day was a nightmare though and, with the 5-Series engine swap underway I just won't have the time and money to restore it, so I'm hoping I can get the £200 I paid for it back from a breaker. That means I'm down about £300 on the whole deal. I could make the £500 back and probably more by breaking the car, but I could really do with it out of the way quickly now so a loss it may have to be.