Hesitation w/ throttle barely open

[kublah]

After a few days of driving and getting used to my car, I've noticed that when I'm just cruising at a constant speed with the throttle just barely cracked, the car will hesitate for a fraction of a second like the fuel supply is being dropped back down to idle level, then quicly jumps back to normal. The result is a fairly uncomfortable surge in lower gears. The car starts, idles, and runs up to red line perfectly otherwise.

I've been through just about every hesitation thread I can find on other forums and the FAQ on twinturbo.net, but haven't found much that deals with this specific issue. All the connections are clean, my throttle bodies just have a little bit of grease built up, nothing substantial, and I get the 55 code from the ECU.

Is it possible that the TPS itself is bad even though there is no code being shown for it? I've noticed a little bit of dry rot around some of the softer hoses, could this be a symptom of a vacuum leak?

Any input would be appreciated.

[<SSR>David]

sorry, I have no idea...B.B I would like to know whats causing your problem also...so I can learn from it ^^

[k3smostwanted]

code 55 just means that the ECU is reading everythign fine.

i would check the TPS...sounds like your ECU doesnt know what position your throttle is at so accordingly the sensor may be malfunctioned.

but it could be a list of many other things...

spark plugs
injectors
fuel filter
air filter
etc

i would put a new fuel filter in it, check the plugs, and run some injector cleaner through the system for starters

[kublah]

Originally Posted by k3smostwanted

i would check the TPS...sounds like your ECU doesnt know what position your throttle is at so accordingly the sensor may be malfunctioned.

That's really what I'm thinking too. I would think that if it were any of the other possible culprits this problem would manifest itself under acceleration or higher rpm's when the demand on the systems would be greater.

How should I check the TPS?

[k3smostwanted]

Originally Posted by kublah

That's really what I'm thinking too. I would think that if it were any of the other possible culprits this problem would manifest itself under acceleration or higher rpm's when the demand on the systems would be greater.

How should I check the TPS?

each sensor has a specific set of OHM values that it is supposed to read within. so you will need a multimeter...i prefer digital and you will need to go to a local Nissan dealership and see if you can find out the OHM range that it is supposed to be within.

but a partially clogged fuel injector would act teh same way...when you give it generate amount of gas...the spray is enough to compensate. same with the spark plugs...

i had a bad plug that was completely blown and it ran perfect once you got it to rev. but when you first jumped on the throttle or let it idle it would sound hesitate very badly.

good luck...

[probehtr300]

i had the same problem and replaced and adjusted the tps and its all good now, but before u buy a new one try adjusting yours, like move it maybe one mm to one side or the other and see if it gets better and then keep moving it in the direction of it running better till it either a)runs perfect or b) thats as far as the tps can be adjusted away from dead center and then u get a new one like me.
But it is POSITIVELY the tps acting wierd

[kublah]

Originally Posted by probehtr300

i had the same problem and replaced and adjusted the tps and its all good now, but before u buy a new one try adjusting yours, like move it maybe one mm to one side or the other and see if it gets better and then keep moving it in the direction of it running better till it either a)runs perfect or b) thats as far as the tps can be adjusted away from dead center and then u get a new one like me.
But it is POSITIVELY the tps acting wierd

Great answer, thanks. I'm glad to hear from someone who's run into this same problem and fixed it. So there's a little play in the connection that might make a difference? I'll mess around with it tomorrow and see what happens.

Here I was getting all excited about changing my plugs & filters and stuff. Maybe I'll do it just for fun anyway...

[probehtr300]

you should probably do all that crap anyways, how many miles are on your Z ?

[kublah]

Just over 65K. I'm pretty sure it needs a timing belt so I was going to have the shop do the plugs and everything when I get around to taking it in for that routine service, but that would just be throwing away money.

[k3smostwanted]

Originally Posted by kublah

Just over 65K. I'm pretty sure it needs a timing belt so I was going to have the shop do the plugs and everything when I get around to taking it in for that routine service, but that would just be throwing away money.

well if you have 65k miles on the stock fuel filter, air filter, and spark plugs...i suggest you change them along with the timing belt. these things are part of routine maitenance that needd changed every so often to keep your car running good.

i would not have a shop do your air filter or fuel filter because these things are pretty simple and shop would milk an extra hour labor out of it when it really takes about 10 minutes each. the spark plugs can be a little tricky but im sure you could do it if you wanted.

[Alphamalez32]

the spark plugs are easy to replace atleast for me it only took me 20 minutes to replace them all and putt everything back.

[kublah]

Okay, here's where I'm at...

The throttle position sensor has been replaced with a new one, and this seemed to help a little bit with the problem. I've also replaced my fuel filter, run a bottle of injector cleaner, and cleaned up a few sensor connections, which were pretty good as it was. The new plugs are still on the to-do list, hopefully I'll get them done this weekend.

But now I've found something I hadn't identified before that popped up when I was getting the new tps lined up. If the engine rpm's are slowly increased from idle up to 2K and I try to hold it there, it will rapidly bounce back and forth between 2K and around 14 or 15 until I run it up past 2. I think this has been happening the whole time and is the cause of the more uncomfortable surges.

My tiny, inexperienced brain is suggesting to me that my crank angle sensor might actually the major problem here. Any ideas?

And thanks for all the help guys...

[k3smostwanted]

Originally Posted by kublah

But now I've found something I hadn't identified before that popped up when I was getting the new tps lined up. If the engine rpm's are slowly increased from idle up to 2K and I try to hold it there, it will rapidly bounce back and forth between 2K and around 14 or 15 until I run it up past 2. I think this has been happening the whole time and is the cause of the more uncomfortable surges.

My tiny, inexperienced brain is suggesting to me that my crank angle sensor might actually the major problem here. Any ideas?

And thanks for all the help guys...

my Z did that same exact thing...i changed my AAC valve which helped for a long time until it came back a few months later. mine seemed to only do it when it rained...it would also get a hgh idle every once in a while.

im sorry though, i cant help you...i just swapped in a new motor instead of fixing it. but when you figure it out, tell me. it will be a peace of mind type of thing.

[kublah]

Originally Posted by k3smostwanted

but when you figure it out, tell me. it will be a peace of mind type of thing.

Throttle body set screw (?) was missing from one side...

I took it to a local shop that specializes in Z's and they tracked it down for me. I don't have the car back yet, but hopefully she'll be running much better when I do.

[probehtr300]

let us know the result