when i start her up cold, she just idles high and sounds smooth, then after it's warmed up, rpm's return to baseline but engine becomes choppy like it's an injector issue. anyone have some idea what could be wrong? car has 120K miles

 

could be motor mounts. Mine does the same thing and gets worse when I put it in drive.

 

Could be an injector, could be a coil pak.

 

check codes, do tune up if you havent in a while.

 

i did replace two each of coil packs and injectors, OEM. but because this problem does present itself until engine warms up(this applies to the car just idling in park; it has real choppy accel. even if you immediately start driving the second you start the motor.)
sorry, sort of rambling. i just would expect this problem to reveal itself right after the motor starts, not after warmup.
also, get this, my CEL had been on for long time(0304) now it's off and bulb not burned out. pulled codes and only get 0304, KS.

 

anyone, please

 

A bad KS will cause a big power loss which could affect your accelleration. When is the last time you changed spark plugs?

 

Tune up would be a good place to start.

-Change pcv valve
-new air filter
-New fuel filter
-Platium plugs
-Trans flush
-Coolant flush
-Service battery (if needed 3-4 years old replace)
-clean ground end of battery wire (which bolts to the engine)
-Clean IAC and TB
-Clean Mass air flow sensor, (Electric parts cleaner just a spray and wipe)
-fuel injection service (Highly rec.)
-scan for codes (pending) if you see any knock sensor codes replace as needed.

then give it 2 weeks for the ecu to adjust to these services and let us know how it runs.

 

A bad KS usually just mean that the ECM will go to a lower amount of ignition timing advance and lose power but not running rough. Probability of 2 things going wrong on a car is not large so replace the KS and see what happens.

 

I would first try all of those listed except the trans flush, if its a clean red there shouldnt be a worry unless you are at 60-70k and have never changed it. Generally from what I have read once you are later in the miles with a trans, if the fluid dosnt look dirty it may actually hurt to change it. But I have a feeling im wrong since i have had a few for the extra large bowl.

 

Sound's dumb but try adjusting the idle, if you have messed with the throttle position sensor, or the idle screw, i just replaced mine and the idle smoothed out and WAY less vibration.
just my

 

my car is basically doing the same thing, and ive replaced the MAF,KS,plugs,coil packs,Crankshaft sensor,air filter,fuel filter and tested the injectors, and i still cant find the problem...only codes that pulled was the knock sensor and the crankshaft and i replaced them, let me know if you find out whats wrong with yours...

 

Same issue here as OP and you... I've only replaced the Air and Fuel Filters at this point, as I found some broken and non-connected vacuum lines, and I need to get those right before I proceed... however I'm curious to see if any one has a determinative solution, as I don't have the time or money to through into this at this time - and I drive it about 50 miles a day...

oh and what is KS?

 

I had this exact problem on my car and it was a single faulty coil.

When I first noticed the problem, it took about 5 minutes of driving to get it to start acting up. I lost acceleration/power and it would chug like a tractor when crawling/stopped. It progressively got worse until it was doing that almost immediately upon start up. I'd imagine it's because electrical components lose conductivity as they heat up.


You can test for a faulty coil by taking a long handled flat head screwdriver and placing it on the coil assembly. Put your ear up to the handle, and if you can hear it clicking it's working. If you don't hear anything, you've found your problem.

 

knock sensor

 

My car had a problem where it would start up good when cold, but when it was hot it would only hit 1000 rpms then stall. I would give it some gas the next try then it would start up. Knowing that it would start when I gave it gas I knew it had to be either Fuel Injectors or Throttle body. So I took a look at the throttle body and it had black deposits all around the inside. Sprayed some throttle body cleaner really good around the plate. Now my car starts up good every time.

 

If the loose/broken hoses don't fix my issue - I do this test and see...

ah, thank you!

This isn't a starting issue, all of the cars with the issue start fine, they 'bog down' under acceleration, chug under deceleration, and overall just barely get down the road at times, most especially noticed 'at temp' (ie needle 1/2 way up), babying the throttle seems to get me down the road, but pisses both me and the other drivers off fairly quickly.

 

What code are you picking up on the OBDII?

 

Have you pull any codes? Your problem seems to matched what happened to my car before the MAF died.

It would be fine when during the first few minutes driving but after like 20 minutes my car would start acting funny and when I step on the gas from a stop it wouldn't go, and then all of a sudden jerk forward, and during deceleration the RPM would jump up and down up and down.

 

AutoZone is a long ways from me, so I haven't gone to get them to pull the codes... I previously had a code for the o2 sensor (pulled a week of getting the car)...

On a side note - can ANYONE explain why this tiny thing (the Knock Sensor) is so expensive... ?? (ranging from about $50 to over $120 in price)

 

I'm having the same problem, my brother in laws father has been service manager at my local Nissan dealer for about 20 years he said even if the code isn't coming up could be an oxygen sensor to test it you have to pinch a return vaccum line and see if it cleans up the idle, pinching the line with a set of pliers makes the O2 run open loop. Gonna try it tomorrow and let you know if it works... I just bought the car and of course it had an engine light guy said it was just the KS but I'll check the codes and bet an O2 is there too

Oddly enough it seems less rough if not completely normal on deceleration


***** sorry misquoted you should pinch the FUEL return line


so I checked my codes speed sensor (knew that) KS and O2 tried the pinch line trick didn't change the engine roughness, I got my money on the KS cause it seems to run better high RPM gonna change the KS see if it fixes it and then the O2 and let ya know

 

You can buy a knock sensor from Ebay for cheap. I purchased one from Ebay 3 years ago and still working fine.