Hesitation at freeway speeds

[faral]

Hello All,

A couple weeks ago, going on the freeway, my 2002 P5 had a hesitation. I wasn't going very fast or slow, about 60mph. I didn't think much of it until it happened again...and again. It has only happened when the car is warmed up, usually around 3000rpm or so. It can happen at anytime, but it seems to happen more when I'm going up a hill. It doesn't happen if I'm going up a hill on cruise control (freeway hill). Happens regardless of fuel tank level.

I cleaned the MAF and the throttle body, and the car did seem smoother and had slightly more umph, but this morning the hesitations were still there. They did seem different, though, sharper and faster. I don't know if it's because I didn't clean the throttle body enough.

I replaced the coilpacks roughly a year ago (but cheapo autozone generics), the spark plugs replaced maybe 1.5 years ago. I cleaned the EGR about a year ago, because of a rough idle, but cleaning it didn't do squat at the time. Both the O2 sensors have been replaced within the last 1.5 years.

No CEL codes thrown (hopefully i won't get any!!). I'm thikning of going to autozone to check if any codes have been recorded even if there was no CEL.

Any suggestions? I've tried searching this forum, but everyone's problem seems a bit different.

 

[thecrash91]

i get the same thing. so far i have replaced spark plugs, and changed from CAI to SRI. its gotten better. do you have any mods? and do you know what the weather was like when it happened? i noticed it would happen a lot more when it was damp and wet out so i assumed my intake was pulling in a little bit of water. also, try changing your air filter if its stock or cleaning it if its CAI or SRI. you could have inconsistent oxyten:gas ratio in your engine

 

[slavrenz]

Hello All,

A couple weeks ago, going on the freeway, my 2002 P5 had a hesitation. I wasn't going very fast or slow, about 60mph. I didn't think much of it until it happened again...and again. It has only happened when the car is warmed up, usually around 3000rpm or so. It can happen at anytime, but it seems to happen more when I'm going up a hill. It doesn't happen if I'm going up a hill on cruise control (freeway hill). Happens regardless of fuel tank level.

I cleaned the MAF and the throttle body, and the car did seem smoother and had slightly more umph, but this morning the hesitations were still there. They did seem different, though, sharper and faster. I don't know if it's because I didn't clean the throttle body enough.

I replaced the coilpacks roughly a year ago (but cheapo autozone generics), the spark plugs replaced maybe 1.5 years ago. I cleaned the EGR about a year ago, because of a rough idle, but cleaning it didn't do squat at the time. Both the O2 sensors have been replaced within the last 1.5 years.

No CEL codes thrown (hopefully i won't get any!!). I'm thikning of going to autozone to check if any codes have been recorded even if there was no CEL.

Any suggestions? I've tried searching this forum, but everyone's problem seems a bit different.

Could be a fuel pump starting to go bad. Maybe the force of trying to pump gas while going uphill, combined with a probably near-clogged fuel filter sock is getting to be too much on your poor little pump.

If not, I'm willing to bet that there is a problem somewhere in your evaporative emissions system.

 

[faral]

funny thing is, it only happens at a range of rpms. mainly between 2k and 3k rpm. and only when the car is warm.

if i drive along at 3.5k rpm, nothing happens. it just goes like nothing is wrong. in 5th at 65, i'm just about 3k rpm, and it'll herk and jerk. if i drop down to 4th, i'll be near 4k rpm going 65ish, and it's totally smooth. loud as hell. but smooth.

a friend suggested the MAF.

i can't imagine the fuel pump would only react at only certain rpms.

oh, and what's the evaporative emmissions system?

 

[slavrenz]

funny thing is, it only happens at a range of rpms. mainly between 2k and 3k rpm. and only when the car is warm.

if i drive along at 3.5k rpm, nothing happens. it just goes like nothing is wrong. in 5th at 65, i'm just about 3k rpm, and it'll herk and jerk. if i drop down to 4th, i'll be near 4k rpm going 65ish, and it's totally smooth. loud as hell. but smooth.

a friend suggested the MAF.

i can't imagine the fuel pump would only react at only certain rpms.

oh, and what's the evaporative emmissions system?

Things like charcoal canister, purge solenoid valve, PRC valve, etc. Sometimes if these become too laden with gasoline they can start to bog down at weird times.

 

[P-Funk!]

i get the same thing. so far i have replaced spark plugs, and changed from CAI to SRI. its gotten better. do you have any mods? and do you know what the weather was like when it happened? i noticed it would happen a lot more when it was damp and wet out so i assumed my intake was pulling in a little bit of water. also, try changing your air filter if its stock or cleaning it if its CAI or SRI. you could have inconsistent oxyten:gas ratio in your engine

No, if it happens only when it is damp - it is usually plug wires or coil.

'water in my air filter' is only a problem if it is 100% water and no air.

bad
bad
bad
bad.

 

[slavrenz]

No, if it happens only when it is damp - it is usually plug wires or coil.

'water in my air filter' is only a problem if it is 100% water and no air.

bad
bad
bad
bad.

And with a stock filter location, I'm thinking that's gonna be the least of your worries.

 

[faral]

yeah, i don't think i have water in my system. the hesitation is coming up too predictably (very specific RPM) for it to be something that can present itself at anytime and any condition

 

[sethro_GT]

If its RPM related use an ohm meter to see if you have gaps in the throttle position sensor.

 

[faral]

where is the throttle position sensor? is that way in the "back" near the cabin of the car?

i looked in my sister's mazda 3...things are just so much more accessible in the mazda 3. what the heck...

 

[sethro_GT]

It will be at the end of the intake duct work on the throttle body. I'd have to look in the manual to see what two pins need to be measured while the throttle plate is opened.