jzzzake

In the am, when I start my car, she will start up and idle perfectly, but when I step on the gas, she will bog down, I can hear a slight popping in the engine compartment. If you keep your foot on the throttle, she will stall out. But if you feather the gas until you can move the idle up to around 2500 or 3000 the hesitation and bogging goes away and doesnt come back until you try to start the car. It happens only at initial start up.
Symptoms - bogging down at start up under throttle. slight backfire, hesitation, no check engine light
Parts already replaced - fuel pump, fuel filter, spark plugs,
Aftermarket parts - Headers, K&N cold air kit
Work done - removed and cleaned throttle body, replaced plugs, fuel filter, fuel pump

Any suggestions?

KrazyK

Jzzzake, just an observation but it would be helpful if you would post your car info, year, mileage, etc. I assume its some type of 996 or you wouldnt be here. It has a fuel filter you replaced so pre 2002? But, you also say fuel pump so who knows what year you have? Who did the work? When? Symptoms before work done? Stored code(s), may not show CEL?

From what you posted, my WAG is:
1.coil packs
2.other ignition problem
3.injector (doubtful)
4.MAF (more doubtful)
5.AOS (unlikely)

And, also IMHO, the K&N is a red flag, headers another red flag. Oops. Forgot, check for vacuum leaks too.

Macster

Deleted.

Hurdigurdiman

Backfire? Doesn't that indicate a wrong air/fuel mixture? Or maybe the timing is out somehow? Now I have no idea what controls those symtoms on these More modern cars but I could solve it on the old beetles in a flash haha. Then again altering the original to Aftermarket parts - Headers, K&N cold air kit, may effect the performance of the engine. Hell I don't know so I had best shut up. Hope you solve the problem. Are you using the top grade fuel?

Pac996

When the headers were done did you remove the cats and or O2 sensors? Does the air pump come on at start?

fpb111

Sounds like lean condition at cold start. Vacuum leak?

mcipseric

check your MAF sensor on the intake.

white99c2

How cold is the temp outside? My car will pull back also as I pull out of the driveway when it's cold outside. When it does I back off the throttle and its dime. Do not rev a cold engine in past 2500-3000 rpm's until the temp gauge gets up to the the 1st line on the gauge. I don't know what year your 911 is but mine is a 99 that first went into service in May of 1998. I go easy on it until the temp is up and then drive it normal. It's a teenager and I am determined to keep it for 6 more years, it will then be a 20 year old car.

jzzzake

The car is a 1999 C2. I live in Key West so the mornings are never less than 65 degrees. I did the work myself, as I own a shop here,there are no stored codes, no CEL, always run the best gas, cats and O2 sensors are still there, air pump comes on at start, MAF working prfectly.

ChristopherG

A bad coolant temp sensor messing with the cold start enrichment possibly.

Hurdigurdiman

+1... My sentiments entirely. I have the same year C2.