Stutter / idle problem help!

[2.5T_/<ouki]

Hey All, thank you for taking the time to read this post. This is my DD so I'm very eager to get this issue resolved. I was planning on getting my tune this December however this problem is keeping me from doing so.

Engine

Rb25
Rebuilt w/ stock internals
Apexi 1:1 HG
ARP studs
Greedy Intake manifold
Stock turbo
Stock Injectors
Q45 TB
FMIC
Aeromotive FPR
Z32 Fuel filter
Walbro 255 fuel pump
3" from turbo back.


Problem 1

Car starts to "sputter" and feel like it's hitting a wall around 5k RPM's. Now I've been reading online that this means my coil packs are going out and more than likely have cracks. I have removed my coilpacks and inspected them very well; no cracks anywhere! I recently changed my spark plugs and after putting the new ones in, car ran pretty good for about a week or so, now back to stuttering badly. It doesn't do it EVERYTIME but it does it a lot, especially while just cruising.


Problem 2

From time to time, my idle will be around 3k RPM even when the engine is fully warmed up. I'll drive a bit and when I finally come to that stop, it will drop back down to normal, however there are times I'll get to the stop light at 3k RPM, and it will rapidly decrease to 1k then bounce right back up to 3k, then back down to 1k. It will do this bouncing up and down until the light turns green and I step on the gas.

I'm not sure if these two problems are related to each other at all, but about 3 months ago I had an idle problem just like this, however the RPM would never decrease and stay at 3-3500k. I had taken it it and had the TPS replaced, now it's doing sort of the same things.

What do you guys suspect? Bad MAF? Bad Coolant temp sensor? Bad ignitor chip? I haven't pulled codes at the moment, but will do so on my lunch today. I have checked for boost leaks and have found 0.

I truly appreciate the help. This is my DD so it's very important i get it running smoothly so I can get a proper tune.

Thank You

[Edwin562]

usually high idle will indicate a vacuum leak, Check around the intake manifold or look for a loose vacuum hose... the jumping of RPMs would have to be a MAF issue, Check if MAF is dirty or wires look beat up.

by any chance did you inspect your old Spark plugs? do you remember the smell or the look?? Spark plug condition will tell alot about whats going on in the combustion chamber..

[2.5T_/<ouki]

Thank you for the info Edwin, and yes I did happen to check the plugs before putting in new ones. They were sort of a grayish color not white from what I could tell, so I wasn't thinking it was running lean, but to be honest I really don't remember the smell. It was about 6 months before I changed the plugs.

Now, as far as the MAF being the culprit, how would I go about checking this without having a spare? I know I can unplug it and if it has no change then most likely it is the MAF, but when doing so, the MAF won't rev past 2500.

I just checked for codes and getting 55, so it's saying nothing is wrong.

Thank you again.

[Tantwoforty]

do you have a wideband?

[2.5T_/<ouki]

do you have a wideband?


No unfortunately I do not. Since the tuning shop has one there to use while tuning, I decided I would save the $150 and put it elsewhere on the car. I don't plan on purchasing a wideband.

Also, I turned the car on, and then unplugged the MAF and the car completely died. I could have sworn it's supposed to stay on just idle like crap and not go above 2500.

Could this be a TPS issue? I haven't volt metered my TPS yet.

[2.5T_/<ouki]

So today i was backing out of my parking spot and my engine just died. It did this to me twice today, luckily i was only pulling out of parking spots and not driving on the roads

[2.5T_/<ouki]

UPDATE:

Got around to testing my TPS & MAF

TPS 5v voltage: 5.1v
Throttle plate closed voltage: .6v
Throttle @ WOT: 4.4v

MAF +12v voltage: 11.5

Could any of these readings be a problem?
Thank you for the help.