Idle issues... cold runs great... after warms up it hesitates... Please help...

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smartbeatz
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Car: 1994 Infiniti J30

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Okay so here's the deal. My car runs great in mornings when the engine is still cold but after I've been driving it for a bit it starts to hesitate. Sometimes even stalls out on me. This is only at stop lights when the car is not moving. I replaced the fuel filter and put in some fuel system cleaner in but to no avail. If anyone can give me some ideas of what it could be I would greatly appreciate it.

Thanks in advance...


GerryO
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IAC valve?

The AAC valve increases the engine idle speed until the engine warms up and then the IAC is supposed to take over, provided it's clean, working properly and the manual idle speed adjustment is set low enough to allow the IAC to control the engine idle speed (should be about 675 rpms with the engine fully warmed up, the transmission in D and fully stopped with your foot on the brake).

Low TPS output voltage is another possibility.

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Infinitiguy19
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1994 Infiniti Q45a 240000 Miles

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I would also like to add that it may also be a MAF sensor.

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infinitiboyj30
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smartbeatz wrote:Okay so here's the deal. My car runs great in mornings when the engine is still cold but after I've been driving it for a bit it starts to hesitate. Sometimes even stalls out on me. This is only at stop lights when the car is not moving. I replaced the fuel filter and put in some fuel system cleaner in but to no avail. If anyone can give me some ideas of what it could be I would greatly appreciate it.

Thanks in advance...
mine does the same thing! when my car is warmed up and i go to a complete stop my idle drops to 600rpm but then when i go to park the car and throw it in park it goes up to like about 800. i threw in a bottle of redline si-1 fuel system cleaner,replaced spark plugs,fuel filter,pcvs,air filter,and even cleaned the air filter box and hoses out and only use bp premium gas and it still does the same thing so i dunno what it can be i think its normal? but im gonna clean the maf sensor with crc and see if that helps if not i give up its just normal cause i know many people with the same issue so f--k it lol

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Infinitiguy19
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1994 Infiniti Q45a 240000 Miles

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OK to tell with out a shadow of a doubt that your MAF sensor is good or bad do the folloing below:

OK the white part in the picture is RTV and can be easly removed.

The red arrow points to the top little black square which you need to remove to expose the MAF sensor's circut board.

Go here to see the picture, click on the magnifying glass to see the picture bigger if needed: http://picasaweb.google.com/lh...tlink

Do the above and then report back with good quality pictures both of you.

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SteveTheTech
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Before you have people cut open a MAF lets try to rule out a few simple things.

You have to take into consideration that this only happens when it's cold, most MAF concerns are seen while cold, under load, or in conjunction with a rough idle conditions. Not to say that the MAF may not be suspect.

Check the ground terminal above the alternator, and all the major connections that are exposed to heat.

Heat in this case seems to be the catalyst. Finding out what is changing while the engine is at operating temperature is key to a quick and accurate diagnosis.

Are there any other symptoms either of you are experiencing before during or after this happens? Erractic electrical component operation(speedo, radio, windows ect.)? Is it a load based surge or something like the engine is starving for air? Or is it like a dead cylinder (noticable at idle and increasing in intensity with applied load)?

These are some random questions and I do not know if they will make sense to anyone other than myself. Let me know and I can reword them.

This is not the easiest thing to diagnose with limited or no access to live data from the engine computer. Blindly throwing parts is an ineffecient way to repair your car and learn how it works all at the same time.

J30 ESM Start reading at page EF-EC 40 this will give you some familiarization with how the J works and the proper steps to keeping it running. Diagnosing the original Infinitis is not easy and their electronics tend to be overkill.

If you decide that the information provided in the link above is a little too much then take it to an Infiniti specialist. Stabbing at things gets expensive if they are done wrong and may damage other more expensive components.

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infinitiboyj30
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i will let you know tomorrow if my idle changed or not. im gonna clean the maf sensor with crc maf sensor cleaner tomorrow and will let you know if my idle is the same.

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smartbeatz
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Car: 1994 Infiniti J30

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Thanks for all the great information...

The engine runs fine when it's cold. After about 10 minutes when the engine is warmed up and I come to a complete stop the idle tends to fluctuate. It will idle smooth for a few seconds then start to jump. When this happens it's like a "erratic electrical component operation" and the lights and radio flicker but do not reset or shut off. What I have been doing is leaving it in neutral with the brake applied and it will not stall and can't jump. If I leave it in drive when the idling starts to hesitate it tends to make the car jump forward. I have the pdf manual so I'll be sure to look it over this weekend. I have gone through it before but could not locate what the problem could be.

I must say I'm really hesitant in taking apart the MAF sensor as it can be expensive to replace.

I would really like to know who decided to put the fuse box in such an inaccessible place. It's a really hard place to get to being 6' 2" and I have lost several fuses in the kick panel.

It's not like the engine is starving for air but more like just the idle drops drastically to stalling. If I hold the gas down a little it doesn't happen at all. I just don't want to keep going through this every time I come to a stoplight.

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yodawill2000
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If the Lights and radio flicker its not the Maf , unless the rpm goes so low the Alternator can produce and your battery is VERY weak.

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smartbeatz
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Update***

If I have the a/c or heater on there is no problem... Now I'm really confused...

I guess I just have to run it with the unit on all the time and just set the auto air high...

ANy suggestions???

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J30inthe sun
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I had a bad TPS recently that made the idle change wildly up & down.

As it got worse it finally threw a CEL. Went to autozone & they pulled the codes for free. It was TPS code.

I replaced it & everything was fine especially after I had my idle air control valve & MAF cleaned.

In case it is the TPS check with Pep Boys, I bought mine there for @$56, less that infinitipartsusa.com & it was the OEM Hitachi brand even though it came in a different brand box.

GerryO
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smartbeatz wrote:Update***

If I have the a/c or heater on there is no problem... Now I'm really confused...

I guess I just have to run it with the unit on all the time and just set the auto air high...

Any suggestions???
Turn ON the headlights lights too. Seriously operating any accessory increases the load on the engine, which the ECM responds to by increasing the idle speed just a bit.

Check/adjust your timing, check/adjust your TPS output voltage and adjust your idle speed screw with the AAC valve temporarily disconnected. Clean your throttle bodies too and how old are your spark plugs?

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infinitiboyj30
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with my j when i go to cold start it it will start right away and idle high and then drop all the way down to like zero rpm and shake a lil and then go back up and stay at high idle i dunno what this can be? this happens to me every morning and its really pissin me off! i have a new battery,new fuel filter,new pcvs,new spark plugs,air filter,etc.

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95-J30tt
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i think the best thing to start with is to read the ECU codes, run the onboard diagnostics, and see what comes up (more than half of the fault codes will not cause the Check Engine Light to turn on)

then take it from there. change the air filter if it needs replacement. did you relocate or modify the air intake, as in, have you installed a cone filter or such ?

check your vacuum lines, turn engine on in a relatively quite area, open hood, listen for any strange air sound (hissing sound) coming from the engine bay, and locate the sound if it exists, most of the time it would be coming from the small black hoses running on either side of the engine (vacuum lines).

ohm your injectors with a multi meter (with the engine off and cold), make sure to set the multimeter to resistance, the readings should not be above 14 ohms for each injector "otherwise, the injector is toast"

clean the IACV (Idle Air Control Valve), it's in the back of the plenum, on the driver side, unplug the connectors and (if i remember correctly, 2 air hoses), and remove 4X10mm bolts holding it to the plenum. clean it and install it back

there are two electrical connectors in the front of the engine (they are on the aluminum coolant hoses leaving the engine in the front centre). basically, they constantly monitor the temperature of the coolant, and send the data to the ECU (if the connectors are dirty, they could be the cause of the idle issue).... take them out and clean the connectors, and plug them back in.

do you feel like your transmission is slipping/not shifting properly??..........check transmission fluid, do that by driving the J for a good 10-15 minutes, then park the car, (make sure that the engine is fully warmed up by then), check transmission fluid level, and make sure that the fluid doesnt have any black particles in it (the transmission could be the issue causing the idle problem, if it is about to go....)

clean the butterfly valves.... with the engine off and cold.... remove the intake hoses where they meet the plenum (2 big clamps), pull the intake hoses out of the way,you will expose the butterfly valves (you will see one on either side), get someone you trust to press the gas fully and not let go while you are working (key should NOT be in the ignition)... spray the butterfly valves with some brake parts cleaner and wipe with a clean cloth that doesnt leave particles behind.

i'm sure there are more simple things that i have missed, but try this out, and update, i hope that this will at least narrow it down.... best of luck

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infinitiboyj30
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95-J30tt wrote:i think the best thing to start with is to read the ECU codes, run the onboard diagnostics, and see what comes up (more than half of the fault codes will not cause the Check Engine Light to turn on)

then take it from there. change the air filter if it needs replacement. did you relocate or modify the air intake, as in, have you installed a cone filter or such ?

check your vacuum lines, turn engine on in a relatively quite area, open hood, listen for any strange air sound (hissing sound) coming from the engine bay, and locate the sound if it exists, most of the time it would be coming from the small black hoses running on either side of the engine (vacuum lines).

ohm your injectors with a multi meter (with the engine off and cold), make sure to set the multimeter to resistance, the readings should not be above 14 ohms for each injector "otherwise, the injector is toast"

clean the IACV (Idle Air Control Valve), it's in the back of the plenum, on the driver side, unplug the connectors and (if i remember correctly, 2 air hoses), and remove 4X10mm bolts holding it to the plenum. clean it and install it back

there are two electrical connectors in the front of the engine (they are on the aluminum coolant hoses leaving the engine in the front centre). basically, they constantly monitor the temperature of the coolant, and send the data to the ECU (if the connectors are dirty, they could be the cause of the idle issue).... take them out and clean the connectors, and plug them back in.

do you feel like your transmission is slipping/not shifting properly??..........check transmission fluid, do that by driving the J for a good 10-15 minutes, then park the car, (make sure that the engine is fully warmed up by then), check transmission fluid level, and make sure that the fluid doesnt have any black particles in it (the transmission could be the issue causing the idle problem, if it is about to go....)

clean the butterfly valves.... with the engine off and cold.... remove the intake hoses where they meet the plenum (2 big clamps), pull the intake hoses out of the way,you will expose the butterfly valves (you will see one on either side), get someone you trust to press the gas fully and not let go while you are working (key should NOT be in the ignition)... spray the butterfly valves with some brake parts cleaner and wipe with a clean cloth that doesnt leave particles behind.

i'm sure there are more simple things that i have missed, but try this out, and update, i hope that this will at least narrow it down.... best of luck
what should i use to clean the IACV? do i have to adjust the idle when i put it back on or just leave the screw where it is? because seriously im sick of my j i replaced so many parts and still the idle is s***ty! when the engine is warmed up and im driving and go to a full stop the idle drops to 600rpm and stays there then when i put it in park it goes up to like 780ish and i think this is not normal. also when i turn the heat on the idle goes up for a while and then drops back to 600rpm and then in a few min it will jump back up?

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95-J30tt
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i disassembled the IACV unit and removed the rubber seals, then sprayed it with brake parts cleaner, then used some WD-40 and a soft brush to clean the hard to remove dirt.....

the idle in your engine is completely normal, when the engine is under load (in gear), the RPM would drop to around 600-650 RPM (it's in the service manual).... and when in neutral or in park it should be around 800RPM.

you can re-adjust the screw on the IACV unit if you need to, but to do that, the engine has to be fully warmed up, and transmission in neutral (i would drive it for a bit untill it is fully warmed up)..... apply parking brakes when you are doing the adjustment..... you need to adjust the screw to a point where the RPM is at 800 when on idle. if your engine is idling at 800 or around there, then you dont need to adjust the IACV screw

hope this helps, good luck


Carlalawson
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Car: 1998 Nissan pathfinder

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My Nissan pathfinder starts and runs great when it's cold but after it gets to normal running temperature and you drive it then it starts skipping really bad and becomes hard to keep running I had it tested and it come up with the knock sensor and I just wanted to see have anyone else had that problem and did changing the knock sensor solve it before I go through all this to put it on

fourdrinie
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the knock sensor issue is probably a lingering issue, have the knock sensor code cleared...and see if your problem still exists and if the knock sensor code comes back right away

Carlalawson
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So it's probably not the knock sensor then what can it be

fourdrinie
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There's a whole host of issues of what it could be, but these engines are plagued with faulty MAF sensors after many miles


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