Low RPM miss? No codes showing...

[TheGrayt1]

I am experiencing a low rpm miss with my 99 GT. I scanned for any trouble codes and there are none. The miss is really at only low rpms and then it smooths out a little when I get on it in higher rpms. I am new to the mod motors and would greatly appreciate a checklist of what to look for and how to resolve the issue. thanks guys.

 

[lvmustanggt]

reset battery and see if it helps, I had bogging problem about a month and just few days ago I change upstream o2 ( both of them) and bamn problem slove.

 

[TheGrayt1]

Wouldn't it throw a code if the o2 sensors were bad. My mods are in my sig, and I also have a Diablo Predator tuner. Should I just clear the ecu with that or does disconnecting the battery do something different?

 

[blackink00]

disconnect the battery, check if you have a vaccum leak anywhere and most likely clean your MAF sensor. lemme know if that works.

 

[fudleyd]

disconnect the battery, check if you have a vaccum leak anywhere and most likely clean your MAF sensor. lemme know if that works.

+1
You might check your PCV as well at this point.

 

[TheGrayt1]

What do you guys clean the maf with? I have electrical cleaner or carb cleaner? Should I run some seafoam in it?

 

[steve_stang2003]

What do you guys clean the maf with? I have electrical cleaner or carb cleaner? Should I run some seafoam in it?

Electrical cleaner or MAF cleaner...
NEVER carb cleaner and as for Seafoam, well, I wouldn't go near that stuff unless you have a very high mileage car that was abused and have tried everything else.

Carb cleaner eats plastic....
Electrical cleaner does not...

Make sure the electrical cleaner does not have silicone in it like some Radio Shack "tuner cleaner spray" does.
That will gunk everything up.

 

[TheGrayt1]

Great I will do all of this tomorrow, but when I was driving the car home it seems that it is only hesitating in gears when under load up until about 2000 rpms then it runs fairly smooth. Has anyone encountered this problem?

 

[poindexternasty]

I have had this problem, my car does the same exact thing. 2002 GT vert, stock

 

[COramprat]

Check the COP's and plugs also...if you have some dampness in the wire you will get a miss.

 

[faststang_728]

Disconnecting the battery only erases the KAM of your PCM. So that just makes your car forget what it has learned.

It could be with your COP or even more likely your EGR is flowing exhaust gas into the cyl all of the time, there for it would clear up around 2000 rpm when the egr is supposed to be flowing at cruise. Does it miss at WOT and idle? If so i would say egr. Look for a DPFEGR PID on your scan tool and see if it is flowing at idle.

 

[cougar694u]

I have this same problem. I changed plugs, wires, but not the coils (yet, heh). I cleaned the MAF, too.

I'll have to check the EGR to see if that's the problem. The car has almost 160k miles, so I thought maybe a clogged injector as well.

 

[4.6andSlicks]

I've got the same problem. Anyone have the solution?

 

[Joshual11]

I am also having the same problem. Just changed the plugs and fuel filter. Still no change. I was wondering if it was some bad gas, but it seems that others are having the same problem. I'm going to try and put premium gas and injector cleaner and see if it clears up any. If that doesn't work, I'm gonna get some eletrical cleaner and clean the maf sensor.

I pray to God that I didn't screw something up when I changed the plugs. I had to remove the fuel rails and I was very careful not to get the injectors dirty or drop anything anywhere, but you never know.

Hopefully, we can figure this thing out.

 

[Cobra123089]

change the plugs, make sure you have either autolite or motorcaft. Are cars can be picky i had the same issue with ngk and bosch plugs.

 

[poindexternasty]

This is probably the "hitching" problem. It may relate to the EGR system in some way. Do some more searches on this forum and others. I don't think there is a solution to the problem.

Let me guess, it does this with slight throttle, low RPMs, and in high gears going 35-55mph?

 

[Joshual11]

Yes, low rpms and 35-55mph. No luck on the premium gas and injector cleaner. Checked hoses. Might have a cracked hose running from the airbox or whatever it's called. It's a short hose about 8" and about as big around as my thumb. What is the name of it? I can't find a replacement for it anywhere. Hopefully this is the problem. If that doesn't work I'm gonna try and clean the maf sensor.

 

[02nightmaregt]

I had that problem and it was driving me nuts. I cleaned the MAF with MAF cleaner, changed the plugs, and even tried disconnesting the battery. Finally i changed both upstream o2's and that was it. The sensors were bad.

 

[poindexternasty]

glad to see we got a resolution for you, 02..... Did you ever throw a code for the bad o2 sensors? Did you replace all 4 of them or just the upstream ones?

 

[hotcobra03]

I would use oem plugs,replace all o2s,turn on o2 with predator.since u reset pcm you will need to drive car so it can relearn fuel trim.for us dummys,your pcm resets itself with a 14 step drivecycle.a 30 min drive at 60 than 30 min city slow drive at 3 different speeds.caution this cruise must be done while very easy driving lite on the gas.after long drive cel might not lite till next restart.follow your cel