Hesitation w/ throttle barely open

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.

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

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

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?

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...

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

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...

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

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.

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.

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

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...

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.

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.

let us know the result

SOOOOOOOOOOOOO much better...

All the hesitation is gone, my idle is back to where it should be, and I couldn't be happier. Time to go for a drive...

awesome man, good to hear you got her fixed.. now lets hope i can get mine fixed too and we'll be golden :thumbsup:

Good luck with yours, I'm sure you'll get it straightened out.

I didn't quite realize it until today when I finally got to drive it around for a while with it running pretty much perfectly, but this car has really gotten into my head. I had a long dream last night about getting it back from the shop where it went back and forth between running perfect and hardly running at all, and then actually catching on fire a couple times. I was on the freeway and there were accidents happening all around me, and I was getting really paranoid about other people hitting me or vice versa. If something were to actually happen to it I would be really upset, and I'm not used to that kind of emotional attachment to my cars...

another one is born!!! :lol:


anyways, did the mechanic happen to say Throttle Position Sensor (TPS) sensor??? was that the screw?

No, the TPS was fine. What I understood was that it was a screw somewhere in the throttle body itself that was missing and allowing something in there to move independently of wherever the throttle was. How this only affected the engine at 2K and slightly off idle is beyond me, but that's why I'm not an engineer.

No, the TPS was fine. What I understood was that it was a screw somewhere in the throttle body itself that was missing and allowing something in there to move independently of wherever the throttle was. How this only affected the engine at 2K and slightly off idle is beyond me, but that's why I'm not an engineer.

throttle adjustment screw was missing?

Well, they used the term "throttle body set screw" when I was talking to them about it on the phone. The work order reads "Left side throttle linkage screw missing" and "Replace left set screw as needed". I didn't have them get into any more detail than that.

Well, they used the term "throttle body set screw" when I was talking to them about it on the phone. The work order reads "Left side throttle linkage screw missing" and "Replace left set screw as needed". I didn't have them get into any more detail than that.

ok...

can you tell which screws or w/e are new ? mabe some pics so if anyone experiances that problem theyll know what to look at.

Well, the car was back at the shop again today with a bad injector, so I had them show me what they replaced.

The screw is on the transverse rod that runs across the front of the engine and opens and closes the valves inside the throttle bodies. Just to the inside of the springs where the rod meets the throttle body, there is a little bracket with a connecting phillips head screw that is oriented vertically when the throttle is closed. That's the one that was missing.

I couldn't find a good pic, hopefully that explains it.

Well, the car was back at the shop again today with a bad injector, so I had them show me what they replaced.

The screw is on the transverse rod that runs across the front of the engine and opens and closes the valves inside the throttle bodies. Just to the inside of the springs where the rod meets the throttle body, there is a little bracket with a connecting phillips head screw that is oriented vertically when the throttle is closed. That's the one that was missing.

I couldn't find a good pic, hopefully that explains it.

yeah...i see what your talking about now. but that one isnt my problem but my symptoms were so very similar. damn Nissan and their bigillion sensors and crap...

damn Nissan and their bigillion sensors and crap...

You can say that again, but I guess that's the price we pay... I was pretty surprises when I found out what it actually was. It just didn't seem like something like that would cause the problems that I was having. I was totally expecting it to be a sensor or something like that.

i had a slight off idle hesitation and poor performance with my 1990 300zx na 2+2 that i just bought. turned out to be the coolant temp sensor connector was all gunked up.