Motronic: Surging At Idle & Part Throttle!
 

I'm having a problem where my engine will surge badly at idle and stall within secods. It also surges violently at cruising/part-throttle, so it's not just limited to an idle condition.

At WOT is *seems* to accelerate fine without surging but I haven't really taken it to redline to ensure it's surge free at the upper end, but it seems fine at WOT.

I can stop the surging at idle by slightly opening the flapper door in the Air Flow Meter with my finger (which makes the mixture richer) so I'm assuming my surging is being caused by a lean condition.

I just had all the inlet manifold gaskets replaced and all vacuum lines seem OK. Also tightened the clamps that joins the two intake plenums.

I have a fuel pressure guage connected to the left fuel rail permanently and it shows the proper fuel pressure at idle (between 36-40psi).

Can the fuel pressure be fine, but the engine still running lean, due to perhaps blocked injectors or something?

If the fuel filter was blocked, the fuel pressure at the rail would be lower, right?

Trying to adjust the brass idle screw at the throttle body makes absolutely NO difference whatsoever.

I've already taken out and cleaned out the ICV/ISV with carb cleaner. Also tested the CHT and it measured up fine (2.8K ohms at room temp).

I'm thinking now maybe my fuel injector(s) are clogged and making the thing run too lean :confused:

Any other ideas please???

P.S: Haven't run an O2 sensor for years, so it aint that.

bump - id like to hear an answer to this

Sorry, I found the problem to be a dud Air Flow Meter. Replacing it with a known good one fixed the problem ;)

Merv:
Can you show your presure gauge mounted on the fuel rail?
j.p.

JP, it's not actually mounted. I've simply had a stainless steel braided line made up with the appropriate fittings and I have the fuel pressure gauge hanging off the fuel rail test port. It's only there temporarily until I resolve these fuel pressure issues, then I'll remove it.

Can you tell me where you bought the 12X1.5 fuel rail fitting?
j.p.

i'm looking for that damn 12 x 1.5 fitting also!

i have another question. what does the fuel pressure do when you blip the throttle from idle?

JP, I just got the whole line with fittings made by my local Earl's Hoses supplier. I just gave him the specs and he made it up for me.

Dougn1, blipping the throttle only affects the fuel pressure by 1 or 2 psi.

I'm having a similar issue with my newly installed 3.2. I have to check the fuel pressure but this description sounds exactly like my car. I call it "Go-fastitis". Its only happy when I'm going fast!

I'll check the above items.