M40/auto surging idle problem

Post Sun Oct 30, 2005 5:41 pm

I bought a 1988 318i Auto today, and the only real problem is what feels like a lumpy idle if you hold the car in drive on the brake. Feels like the engine keeps surging. I've changed the leads a plugs but it's still doing it. Any ideas or is it a case of, "They all do that mate"? It's the M40 engine.

Thanks in advance

Post Sun Oct 30, 2005 6:34 pm

Just to add, it is a bit lumpy at idle when in park/neutral but fine once it's on the move. Would it be worth changing the cap and rotor arm?

Post Sun Oct 30, 2005 7:16 pm

it sounds like a air leak again check the hose from the air flow meter

Post Sun Oct 30, 2005 9:26 pm

optima wrote:it sounds like a air leak again check the hose from the air flow meter

I've just taken the hose from the AFM to the throttle body off, and examined it, and there are not tears in it, so it's not that. Worth checking though.

Post Sun Oct 30, 2005 9:52 pm

I had similar surging with an M40 and replacing the fuel filter cleared the problem completely.

Sharknose

Post Tue Nov 01, 2005 5:45 pm

Thanks for the help so far guys, here's an update.

I've so far changed:

Sparkplugs,
Plug Leads,
Fuel Filter

I have cleaned with carb cleaner:
AFM
Throttle body (didn't take it of, just sprayed into the body with the throttle closed and open)
Idle Control Valve

It's running slightly smoother, but not much. The surging when held on the brakes in drive is much better, and will be perfect if I can sort the lumpy idle.

I've pulled the plug leads off one by one with the engine running, and they all cause the engine to run rougher.

I've had the cam cover off, and the cam looks in good condition.

I've done a compression test:

1 = 161 psi
2 = 165 psi
3 = 165 psi
4 = 165 psi

I'm running out of ideas. What would you check/change next?