Throttle Position Sensor help

Hey guys,

Got a new problem with my little micra, the throttle position sensor stopped working and was returning no value at all on the diagnostic software. Idle was bouncing around all over the place. Got a couple of spare throttle position sensors that were in a job lot of things I bought from a friend, anyway I've fitted one to the car and the idle has returned to its normal 640 rpm but I now have a cylinder 4 misfire that happens at idle. It doesn't throw the dreaded check engine light on but appears as a pending code on my diagnostic software. I did notice however that the ignition timing advance at idle will not sit at 15 degrees. It jumps around between 11 and 18 degrees.

I can get it to sit at 15 degrees by loosening the sensor, adjusting its position and tightening the little screws. Doing this stops the misfire happening. If I turn off the engine then restart it the ignition timing returns to its state of jumping around and the misfire coming back.

My question is there a specific way to set/calibrate the throttle position sensor?

Thanks
 
OP
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radarcomp
UPDATE: The cylinder 4 misfire disappeared for a couple of weeks and then came back so I opted for to have a compression test done when the car was in for a front exhaust pipe replacement. Compression test was fine and generally the engine seems in pretty good health, there are no vacuum leaks. It seems like its definitely down to the throttle body causing problems. Bearing in mind that the throttle body was from a salvage car and I didn't know its history it seems like the likely suspect. The mechanic that I took it to for the compression test seems to agree because turning on the rear demister and having the heater blower on the first setting totally removes the misfire problem. So I'm beginning the hunt for a decent throttle body.

I have a question though that I'd like to get an answer to if anybody knows and that is can I use a throttle body that has cooling pipes on even though the car I've got doesn't have a throttle body with cooling pipes? Do the cooling pipes have any effect on a car that doesn't have the cooling pipes?

Thanks in advance

Rob
 

frank

Club Member
i doubt if the coolant pipes will make any difference rob, and if the cyl 4 missfire disappears when electrical load is applied then i would suspect a coilpack or ecu issue personally
 
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radarcomp
Thanks for your input Frank, looking at pictures of the coolant pipes on a throttle body they just seem to go through the throttle body, being honest I can't see the point of them but wanted a second opinion anyway.

I have had the coilpacks swapped around on different cylinders and the problem didn't change from cylinder 4. I bought a new coilpack and it didn't make a difference. Interesting thought about the ecu though. What in particular on the ecu would cause the problem?
 
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radarcomp
I never thought about the ecu being the problem. Are they particularly easy to change? And more importantly how easy are they to get?
 
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radarcomp
Ah, got you now. Definitely worth exploring. Thanks Frank, I'll let you know how I get on. On the brightside while the misfire disappeared I had the car MOT'd and she passed with flying colours, no rust or nasty oil leaks etc so as you can imagine I'm keen to fix the car and keep her on the road. Kind of fallen in love with this car, more than I have with much more powerful cars I have had in the past.
 

pollyp

Club Member
does the engine use a coilpack or distributor?

the pre-face distributor type TB has coolant lines going through a waxstat fast-idle cam mechanism.
it's a very old tech where the coolent temp affects this wax plunger like in a thermostat which acts on this spring loaded cam wedge which affects how much the throttle butterfly can close.
when cold, the cam keeps the throttle cracked open abit to fast idle. when hot, the cam allows the throttle to return fully closed.
problem is the old wax will seize, the throttle remains wedged open abit and cos the TPS is linked to the butterfly, this'll affect where the ECU thinks the throttle is closed.
and another factor is the idle control valve does exactly the same fast idle action so the waxstat really isn't required.

my usual recommended advice for the pre-face TB is to remove the fast idle cam mechanism so the throttle can fully shut close,

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then adjust the TPS till it reads below 0.5kohm,
clean the IACV head and check the bearing swings smoothly,
calibrate the IACV so that when you force the IACV to 0deg in diagnostic software, the valve head is JUST about closed.
while TB is out, spray clean the MAF with carb cleaner,
check the 2-pin coolant sensor is within oem spec. https://www.micra.org.uk/threads/pollymobiles-rebuild.35251/page-119#post-704079
check neutral switch is working.
check spark gap is clean and 1.1mm
remove dizzy cap and wirebrush white oxide off the 4 points till bare metal.
warm up engine,
check O2 sensor is working fast enough,
clear self learn and give it afew mins to relearn,
adjust idle bleed screw till 700rpm,
force timing at 15deg (in nissan datascan, active tests you click "set base idle")
match crank timing to 15deg IGN timing using strobe gun and rotating the dizzy, readjust idle screw after each timing adjustment.

all explained here:
https://www.micra.org.uk/threads/pollymobiles-rebuild.35251/page-19#post-446256

btw when turning on extra electrical loads like demister, fan, lights, AC, PAS, the ecu detects and tells the IACV to raise idle automatically to compensate for the extra alternator load.

if it's a repetative consistant misfire only on cyl4, and compressions good & equal, check all the plugs are making the same clean blue spark, swap around the spark plugs, swap the 3rd-4th injectors, see if the misfire changes cylinder after these swaps. try replacing the HT leads.
a random coughing misfire could be dirty blocked injectors.
 
OP
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radarcomp
Hi Paul thanks for the input. Mine is the coil pack version. A late 2002 model, registered in 2003. I've had the injectors swapped around. Spark plugs have been changed and swapped around too, and the problem stays with cylinder 4.

The only time it misfires is at idle. Almost like there's not enough air for the fuel. The idle sits steady at around 640rpm occasionally 680rpm switching any electrical item on and it rises to 720rpm occasionally 760rpm. The ignition timing advance at idle is anything but 15 degrees. It constantly moves between 12 degrees and 17 degrees. The only way it is semi stable at 13.5 degrees timing is when electrical load is applied via the rear demister etc.


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frank

Club Member
on the pre-coilpacks the ecu can also use spark advance to control the idle rob (maybe yours is the same)
i had deleted the idle control valve on my turbo k11, so the timing would advance to 25ish btdc iirc when the engine was cold, then would settle at 5 ish once warm
 
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radarcomp
I'm beginning to think that you may well be completely right frank that the issue I've got lies with the ecu. I think I might just take a punt on getting a different ecu. I've seen quite a few on eBay cheap enough. Although they don't come with the black transponder receiver around the ignition barrel, would that matter given I have one in my car already ?


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frank

Club Member
if your idle control valve is,nt stabilising the idle properly tho, then the spark timing back-up system will kick in (not an ecu fault)
have you tried swapping 3 and 4 sparkplugs and injectors ?
and no you need the full ecu kit eh
 
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radarcomp
I assumed that because the idle rises when electrical load is applied that the idle control valve is working properly. Yeah injectors and plugs have been swapped around too.


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frank

Club Member
the icv should have enough scope to cover electrical loads and power steering loads, but i think your stepper motor type have to be set via obd
if the icv is maxxed out for some reason then the spark timing will fluctuate eh
as for why its only affecting cyl 4, i dunno :)
 
OP
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radarcomp
Makes complete sense to me that it could be maxed out. I think given I've got the patience and the money to spend that I'll get a different throttle body and possibly a new ecu after that if the problem doesn't disappear and failing that a trip to my local Nissan dealer might be on the cards.

Not gonna give up on the car, I'm sure it'll get sorted soon enough. Thanks for all your input it's been much appreciated.


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frank

Club Member
the icv is just a finely controlled airleak into the inlet mani basically, so a leaking vacuum pipe or gasket can be enough to max it out eh
 

frank

Club Member
my pre-coilpack k11,s had 1 big one for the brake servo, another big one to the crankcase breather valve, 1 small one for the fuel rail, and 1 small for the carbon canister purge valve rob
 
It's probably an earth issue, as when you turn on the extra electrical items, the coilpack,ecu, or whatever is the problem is finding a better route to earth.
 
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