Surging idle when cold, running ?rich

aap1966 · Post by **aap1966** » Thu Aug 20, 2015 4:12 am

Hi All,
I don't like to beg, but.........I need the Brain's Trust on this one.

I've had a 1989 auto since 2006.

It has ALWAYS run rough when cold, mainly manifest as a surging idle in drive or reverse, not nearly so bad in Park. Also, the smell of unburnt fuel in the exhaust is very (as in VERY) obvious. This all settles down after the first few minutes of driving, but is bad enough to make reversing the car out of a driveway bloody annoying.

The car does about 100km (60 mile) per week.

New injector valves 2010, new carbon canister and plugs 2013, new Idle Control Valve earlier this year. All the gear is new. (The injector valves were meant to be new, but I have subsequently discovered that shop had some dubious practices).

The new Idle Control Valve made a huge difference for about 2 days, then back to where I was.

There are no shops in Brisbane (that I know of) that are really up on 1980s BMWs.

So guys...................... what's the next step?

Thanks in advance.

Brucey · Post by **Brucey** » Thu Aug 20, 2015 9:13 am

a surging idle is almost invariably some combination of

- a faulty ICV/controller
- a badly set throttle body

These cars do run rich when cold anyway but this will be exacerbated if

- the cold start valve is leaking, or cranking is prolonged for some reason
- the CTS is bad (or has a bad contact)
- wrong/bad main injectors fitted
- the AFM is bad
- the FPR is bad

You don't say if your car runs closed loop (ie has an O2 sensor and a catalyst) but IME cars that do can develop all kinds of appalling fuelling errors and the owners just live with them 'because it is OK once it warms up'. Owners of open loop cars pretty soon end up with cars that barely run if similar fuelling errors occur.

cheers

miklilmag · Post by **miklilmag** » Thu Aug 20, 2015 11:55 am

Hello,
Always check, confirm what Brucey's suggests,
But keep it simple, first check for
vacumleak, big one, sucking air with in the system, check if the rubberhose under icv is connected (back fire will make it pop off), holes or/or rips in vacumlines, ...... are all the valve cover bolts there, gasket visible under cover, does taking oilcap off make a different, or pulling oil dipstik, gas cap tight, .....returne fuel line properly connected to gas tank?
Also faulty, wrong Fuel injectors are mentioned, needs checking!
Since you mentioned challenged mechanic! Proper spark plugs!

Just open the and hood give it a good visible inspection, then start digging,
Good luck!

Franke

aap1966 · Post by **aap1966** » Thu Aug 20, 2015 11:44 pm

Thanks for the prompt replies...very much appreciated.

It's 'closed loop' (O2 sensor & catalytic convertors). I've checked the hoses etc. Actually replaced all the old stuff with new hoses shortly after I got the car.

Now, mechanics are well outside my fields of expertise (such as they are), so it's best to assume (I hope) intelligence, but ignorance.

- faulty ICV/controller?? What's "ICV"

- the CTS is bad "CTS" ?? (Being BMW, I assume it's "Currency Termination Service", but I may have that wrong)

- the AFM is bad: Are these specific to national models? My car is essentially UK spec, would it take a US spec AFM?

- the FPR is bad: Sorry, I have no idea what an FPR is.

Yeah, Yeah, I know. Still on the initial upswing of the learning curve, but I'm trying. On the other hand, if any of you guys ever need help with specimen-level phylogenetic analysis of Diplodocidae, just ask.

nick88highline · Post by **nick88highline** » Fri Aug 21, 2015 9:19 am

I had a very similar issue with my 88 car. When absolutely cold, it would start up and idle fine, but as soon as it went into D or R, it would surge. If you left the car to idle for 5 mins or so before putting into D or R, it would be ok. The CO emissions were on the high side at idle ~3% which suggested rich running. I found that if I introduced an air leak, like removing the vacuum line to the interior temperature sensor, it would fix the problem and the idle would be fine. I tried everything except the AFM. Nothing fixed it. Then I decided to try the AFM and that fixed it! I bought a new one, which ran much, much leaner (probably just due to the spring tension being different) and that fixed the idle issue and high CO reading, it's now around 0.7%. Either try getting another AFM, or change the spring tension to lean out the mixture, as you're clearly running too rich.
By the way, my car has no emission control system.

sansouci · Post by **sansouci** » Fri Aug 21, 2015 1:19 pm

CTS Maybe cam timing sensor but I doubt it
ICV idle control valve. Clean the electric contacts
AFM Air flow meter
IMHO in my humble opinion
DFK Don't fkn know

Brucey · Post by **Brucey** » Fri Aug 21, 2015 8:15 pm

CTS coolant temperature sensor.

BTW if your car was factory fitted with an O2 sensor it will differ in a few key respects to a UK spec car. If an Australian spec vehicle it'll be a bit heavier, too; the doors have extra reinforcement in, amongst other things.

cheers

aap1966 · Post by **aap1966** » Sun Aug 30, 2015 8:24 am

OK, guys.
Going for a reconditioned AFM.................I'll let you know.

Brucey · Post by **Brucey** » Mon Aug 31, 2015 6:32 am

you can test an AFM using a DVM so I'd suggest that you do that before shelling out for a new one.

I'd also suggest that you check everything else first, too.

If you start playing 'parts change bingo' with no diagnosis of a real fault with the part you are replacing, it is gonna get very expensive, very quickly.

cheers