Thread: slight bog under acceleration, only making half boost

I just picked up a 98 gtp to do some work on, however without a good scan tool this has got me puzzled. The car runs fine after 2k rpm, when you first step on it it stumbles a little bit and then pulls decent. Im pulling a p0102 code with my pocket scanner, all the wiring to the MAF looks good, and i was told the MAF was replaced a couple years back. Another thing im noticing is that under WOT the DIC is only showing half boost, at redline it sounds like the belt is slipping to me but its making a loud squealing noise at redline. Any input would be great guys, thanks for your help

Well I wen through this morning, replaced my pcv valve, the pulgs, wires, and redid all my vacuum lines and connectors. The car seems to run better up top now, but it doesnt come back down to idle if you rev it in park or on deceleration, it bogs and almost stalls. I disconnected my IAC motor and its coming back down to idle now but at first snap of the throttle its as if it cuts out for a second and then everything is okay. any thoughts?

maf?

ill have to look into that tomorrow, i have a spare gp sitting here i can swap parts from, the one in the car now says "remfg" on it so i would assume its been replaced at some point but i will check that out. Went to leave tonight after the car got cold again and i couldnt get it to run with the IAC unplugged, it kept falling out so i plugged it back in and it idles, just bouncy and seems low to me, needle rests about 600 rpm, and still runs fine up top

IMG 0065 - YouTube

here is a video i took of the car this morning, the idle seems really low to me about 650, when i first hit the gas you can see the rpms drop this is when the car bogs down and then its fine immediately after. After i get it up to 30 and let it come back to idle, the idle seems really choppy and fluctuates a ton. maybe this will help, im lost

the boost guage in the DIC reads from the map or maf depending on which the PCM is looking at, unplug one at a time and drive around to see which one is faulty, i would unplug the MAF first since it is the more commom of the two to fail

well i got access to a good scanner, MAF is bad, steady voltage reading? all the time never changed. But next question is will this cause me to only read half boost

replaced the maf, and still have a choppy idle after the relearn, when up to temp ican unplug the IAC and idle jumpes to about 1200 but stays steady. Is this an indication the IAC is indeed bad? and I still have a vacuum leak I can hear inside the car, it seems to be coming from the vacuum block for the hvac under the dash behind the glovebox, has anyone ever tried using rtv to seal a vacuum leak and had success?

unplug it from the motor and cap it off thats what i did. and unplug you bbv soleniod

i got it capped off, cant hear the leak inside the car, but it seems like every time one thing settles down, another issue arrises. i hope someone can help me out here, It seems like the car runs okay when its fired on a cold start, idle jumps around for a second and then evens out, and the car drives fine. after it warms up, it starts a hesitation when taking off from a stop unless you really mash the gas, coasting to a stop sign the car stalled on me, but started right back up. No codes present. I just changed the plugs with an al606 gapped at .60, any chance the gap could have anything to do with this, or possible bad ICM? thanks for any help

replaced all thre coils this morning, all of them were out of spec on the primary side. no change, still huntoing for idle and tech 2 ois counting misses on all 6 cylinders, and even out at higher rpm. im lost, time to send it to the dealer.

this car didnt have the oversized pistons in it, my old 98 had the punched out motor lol. I had the icm tested, it came back good 12 times in a row, even when it was heated up with a lighter. I replaced all three coil packs which were over spec on the primary side, and sent it back home to chicago. Still had the miss at idle, but without a scanner it wasnt worth throwing parts at. Ill take another look in may when its warmer outside

Originally Posted by mskram1

oh and you get a tune for those oversized pistons??? not sure it needs it but youd think oversized pistons would change compression and displacement causing pcm issues???

a cubic inch or two wont make any difference when split between 6