oups59

This is the last thing on my repair list (at least for this year...)

When in neutral, if I quickly nail the gas the engine hesitates/stumbles for a second then revs up nicely. If I nail it quick enough then let off, I can have my foot off the pedal before the engine has a chance to get going. If put my foot slowly (normally ) on the pedal to bring it off idle, it respond normally. Bringing the engine just off idle, then nailing the gas results in good response though. What gives?

928porschepatrick

I have the same problem don't know what it is
Do you have pops in your exhaust when doing it a few times??

John Speake

Could be an aged MAF not giving the right response to give the required enrichment necessary.....

oups59

Pops ???

oups59

The MAF was rebuilt 4 years ago ( Injection Labs ).

SeanR

Sounds like bad MAF or nice air leaks. Check your hoses under the intake and the Y connectors at the MAF boot.

928porschepatrick

like little backfire

Koenig-Specials 928

I have exactly the same issue. They're like little backfires. I swapped for a good MAF and those symptoms went away, including my acceleration became crispier. So instead of replacing/rebuilding the MAF I am contemplating going to the MAF-less Alpha N from JDS after I've saved up for it.

John Speake

Well it should be good for 75k miles or so...... the symptoms you are getting are of a weka mixture when the LH goes open loop to allow acceleration enrichment. Too little enrichment and you get the hickups :-)

So look for airleaks into the intake as Sean suggests - check engine vacuum on the front damper at idle - should be around 21"Hg at sea level.

Check fuel pressure, check temp 2 sensor....

the flyin' scotsman

Luc.........first, make sure all the basics are covered; spark plugs, disti caps and rotors, air and fuel filters.

As Sean suggests look for vacuum/air leaks, fuel pressure etc.

Did you install the PEMs? how old are the injectors?

Fontana

I was having this problem, I pulled the MAF and noticed the black plastic cover had some minor pits from the engine heat. It was also not sealed well at all as I could easily remove the cover with basically no effort. I sealed the cover shut with clear silicone as well as filled in the pits with silicone and it solved the problem completely. I guess it was allowing unmetered air to get in.

Fontana

Here is a pic the way i found it...

Bill Ball

Some more results from your fire?

oups59

Hi Malcolm,

How was the trip to Kansas ?

Plugs and wires changed this spring, Distributors and rotors have less than 10,000 miles (checked also this spring) fuel filter changed 2 years ago. Air filter is almost new. O2 sensor changed 3 years ago with OE Bosch unit

I will recheck, as Sean suggests, fuel pressure and air leaks but when I checked those a couple of weeks ago, pressure was good (I have a fuel rail gauge) and vacuum was steady at 20 Hg. I also check the fuel pressure regulator (removed the vacuum line and fuel pressure rise witch is normal) and dampers (no fuel smell or leaks).

I don't know if this is related but when driving around town, idle speed is not obtain instantly when in neutral - it stays at 900-1000 RPM for a few seconds than drop to 675-700 RPM. Idle is stable.

PEMs are installed. Concerning the injectors, I don't know. Looks original.

The only modification is a x-pipe without cats.

BRB-83-911SC

I am following this with interest. I have the same symptoms - a bit of "delay/stumble" when blipping the throttle from idle in neutral. I have no "popping/backfire". I also have a slight miss just off idle ~1,200 - 1,500 rpms, which results in slight "bucking" while driving at low RPM, say in a parking lot. Very smooth and resposive otherwise.

Newly rebuilt MAF, new rubber boots (MAF, throttle body, intake runners), newly cleaned/tested injectors, new caps, rotors, Beru plug wires, plugs. Symptoms were present before all of this recent work.

My car is a 16v Euro LH, bone stock, no cats or o2 sensor. It does not do this when engine is cold, only when warm. I am thinking it is a bit lean just off idle.

Looking forward to what you find.