Performance of a 318i

Fri May 22, 2009 12:29 pm

Hi,

When I first got my 318i in December, it seemed fairly nippy. But recently I've noticed it's become sluggish up until about 3500rpm, when it all of sudden takes off! It does seem a bit underpowered up until that point.

On a long run up a hill, occasionally I've had it jolt and almost cut out (only for a split second - almost like I've very quickly hit the brake pedal) and seems to struggle a little bit. When I start it up, it goes to about 2000rpm and the gradually settles down.

I'm sure it wasn't like this when I first got it. Plugs have been done but that was in Feb and I'm sure it wasn't doing this then. Any ideas?

Thanks,
Graham.

Fri May 22, 2009 1:20 pm

not sure but id give it a good servie change all your filters and see how it goes

Fri May 22, 2009 2:26 pm

Always difficult to diagnose from these sort of descriptions, but check out the distributor cap and the rotor arm.

Fri May 22, 2009 2:31 pm

don't forget the usual check for splits and cracks in the inlet hoses

Fri May 22, 2009 2:49 pm

gareth wrote:don't forget the usual check for splits and cracks in the inlet hoses

That as well, and check out the operation of the throttle position switch, while the air hose is off.

Fri May 22, 2009 6:18 pm

OK, thanks everyone. Sorry I can't give a better description - I know it isn't easy trying to diagnose a problem with nothing particularly clear to go, so I do very much appreciate your efforts all the same.

I'm quite new to this, so I don't know where the throttle position switch is or what it looks like. Up until I got the E30, the most modern car I'd ever owned was a 1976 Mk2 Escort, the oldest being a '59 Beetle! Strange as it sounds to say it, but I'm not used to this much 'technology'!

I did the air filter and oil filter (along with a full change to Fuch oil) back in about February/March so it shouldn't need it. Although I didn't change anything in the way of fuel filters.

Thanks,
Graham.

Sun May 24, 2009 5:13 pm

OK, I've had a prod around. Looked at the plugs - nothing unusual there. I'm thinking maybe replacing the fuel filter might not be a bad idea sometime in the future. Haven't been able to look at the cap and rotor yet as I've run out of time for this afternoon and it looks a little awkward to get off so I don't want to be rushing it.

I did, however, find these two things hanging around. I'm assuming they should be plugged in? I found where the first one should go, second one I'm not sure about:

Again, this is new to me so I have no idea what these are or how important they are.
Cheers,
G.

Sun May 24, 2009 9:50 pm

in the bottom pic if the plug is coming from the afm it isnt used unless your car has a cat. if it did it would plug into a charcoal canister.. not totaly sure bout a 318 but thats the set up on a 316..

Sun May 24, 2009 10:17 pm

VolksPikey wrote:I did, however, find these two things hanging around. I'm assuming they should be plugged in? I found where the first one should go, second one I'm not sure about

Second one isn't used (as above).
Are you saying the first one was disconnected? If so, where did you connect it?

Mon May 25, 2009 12:00 am

Brian: yeah, first one was disconnected and I've found the matching bit that it appears it should connect to, but I haven't reconnected it yet. Thought I'd ask first!

Mon May 25, 2009 1:00 am

Is it directly below the engine end of the big air hose; on the bottom end of the throttle shaft?
If so, it's the TPS connector, and your engine isn't going to run correctly with it disconnected!

Mon May 25, 2009 12:08 pm

Hi Brian,
Yep, that's the one. I was basically checking over the big air hose and happened to look underneath it at the engine end. I saw these three prongs and wondered what should be in there, then I spottted the thing hanging down!

Right firstly, breakfast, second, reconnect that thing and see how it goes! I'll let you know.

Cheers.
G.

Mon May 25, 2009 1:05 pm

OK, plugged it back in and started it up. Rather than sitting at 2000rpm and gradually settling down it didn't go as high and settled down almost instantly. It seemed to run smoother as well.

But it is still doing this weird labouring thing up until about 3500rpm, when it takes off. I tried accelerating harder up until that point but it just feels almost like it's restricted and feels like it's misfiring until it hits 3500 when it suddenly speeds up. Strange. Think I need to look at dizzy cap and rotor, plus this throttle position switch you mentioned.

Mon May 25, 2009 9:55 pm

The next questions are: why was the TPS disconnected and has anyone been 'adjusting' the idle speed by playing with the throttle butterfly stop?
The TPS contains two microswitches. The three pins are one common connection to each switch, and one pin each for the other terminal of each switch.
With the throttle closed, one of the switches should be on, and the other off. Just after you move the throttle of its stop, the switch that is on switches off, and as you approach around two thirds full throttle, the other switch switches on.
Use a meter to check that these switches are doing what they should.
If the throttle stop has been played with, the idle switch might not be 'on' with the throttle closed, or it could just be faulty.