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Odd Hesitation From Idle - Request The Help Of The Gurus :)

TUF250

By TUF250,
in Engines & Forced Induction

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TUF250 Proficient

TUF250

Posted
Posted

Hi all,

I have a manual r33 gts-t.

The car is low milage, std with a turbo back exhaust, bmc filter (just installed last week)

I also gave the car a full service when I bought it 4 weeks ago. (new iridium plugs, cleaned the afm all the oils, timing belt etc)

Yesterday I had the 3inch dump pipe installed to finish the exhaust system and had an alarm installed in the afternoon (professionally). I only say these because maybe they are relevant?

No today, specifically tonight an odd problem has emerged. The car is running great, very strong, no missing or coughing, everything is great except....

When you leave the lights and touch the accelerator (no matter weather its firm or soft) the idle drops down about 100-200 rpm before it picks up, this has on occasion casused the car to stall. Its very annoying because im getting nervous everytime I leave the lights.

Is this a common problem? any ideas what it would be?

Interestingly it dosnt happen everytime, probably 4/5 times though, it might be worse when hot but im not sure about that. The car idles (when hot at about 650) which it has doen ever since I bougth it

Please help, open to any constructive suggestions.

Thanks all.

Wheezy Mentor

Wheezy

Posted
Posted

I am thinking now that the exhaust is more free flowing that it is running a little rich.

What temps do you see?

Failing that as ash said something electrical like airflow metre, it might just need a clean with contact cleaner.

O perhaps throttle position sensor. They tend to stuff up. A multiple metre could tell you more about the voltages.

Measure then at idle and at light acceleration. (can only really do this in your driveway with the car standing stop and no load on the engine, unless you have an aftermarket computer and tuning software)

TUF250 Proficient

TUF250

Posted
  • Author
Posted

well the afm was cleaned very well only a few weeks ago so it should be clean unless its failed.

I checked the tps, ignition on and it was 0.39v

I did a search here and found that it should be 0.4 - 0.5v so I adjusted it to 0.5 exactly. I took it for a drive and it now idles at 1800rpm! when I get home tonight ill back it off to maybe 0.45v and see what I get. Was also reading about the ACC valve cleaning which I might look into. Is there a basic idle speed screw on the rb25?

The Dan Grand Master

The Dan

Posted
Posted

What is the fuel pump doing when you touch the accelerator?

Put on a pressure gauge and see if the pressure drops. Also check for vac leaks but if it's pulling strong, then this may not be your problem.

Failing that, take it back to whomever installed the alarm and tell them it's playing up since the install. I have seen alarms temporarily cut power to fuel pumps when they piggyback the power sources from low load items.

XRATED Veteran

XRATED

Posted
Posted

I'm glad to see your looking after your car and not just throwing go fast parts at it like -ALOT- off 33 owners.

Is the BMC filer a dry filter or an oiled filter? If it's oiled, take it out and re-clean your AFM.

Just check your AFM plug for corrosion, also check the AFM wiring harness- checking for cracked/split or stretched wires.

Borrow a fuel pressure guage and mount it to the outside of your windscrean so your passenger can see it, then go for a drive... you have to watch to see if it dips to low on accel. If it dose, ask your alarm place to re-wire the power supply for the alarm... or take it out.

Good luck buddy

Cheers

Justin

TUF250 Proficient

TUF250

Posted
  • Author
Posted

thanks for the replies guys.

The BMC is oiled but it is very dry, I also borrowed an AFM cleaned it and put it back in. No difference, so that has been ruled out.

I set the TPS to 0.42 with engine off and it reads 4.1v at full throttle so thats in spec and still made no difference, although it did pick up the idle a touch which it needed. (now sits at about 700 when warm.

I was doing another search and the ACC valve seems to be a common problem when dirty. I will buy myself some brake cleaner and gasket sealer and give that a good clean tomorrow night becuase its an easy one. if that fails to fix it fuel supply will be my next thing to check

thanks for the input guys

TUF250 Proficient

TUF250

Posted
  • Author
Posted

ok time for an update.

Swapped AFM for a spare and same problem.

Tested TPS voltages and they are 0.42 at idle (engine set to on) and 4.1V when I open the butterfly by hand. This is normal I believe.

I cleaned the ACC valve as per the tutorial in the maint. section and it has improved the hesitation slightly but not fixed it. It does it slightly still. It wants to stall when you slow down quickly but is now less inclined to stall when you take off although its not perfect. The other problem is that it is now idle hunting (more so than before) idles at about 650ish and then speeds up to about 800 and then slows back down to 650. up and down, up and down.

Whats going on? what am i missing? any experiences woul dbe appreciated

thanks

Jason

TUF250 Proficient

TUF250

Posted
  • Author
Posted (edited)

also note, it is dfinately worse once it has warmed up. really need a hand here guys thanks

does anyone have a spare acc valve and TPS that I can buy off of them? will pay for shipping from anywhere

thanks

Edited by TUF250
The Dan Grand Master

The Dan

Posted
Posted

These are not your problems.

The AAC is only active on cold start, the IAC and AAC are both null and void when you crack the throttle anyway and the TPS voltage is fine.

Have you checked to see what the fuel pump is doing yet?

Also, block off or cancel out the charcoal canister to see if that does anything for you

TUF250 Proficient

TUF250

Posted
  • Author
Posted

thats is my next stop. Interestingly after I cleaned the AAC valve the car still had the fault, I reset the computer and redid the earth point as I wasnt happy with it and this morning it was fine. But I dont feel too confident yet, it might redevelop. Where can I get ahold of a new fuel pump and what brand is recommended? The car will remain relatively stockish so no need for an upgrade I would have thought

The Dan Grand Master

The Dan

Posted
Posted
thats is my next stop. Interestingly after I cleaned the AAC valve the car still had the fault, I reset the computer and redid the earth point as I wasnt happy with it and this morning it was fine. But I dont feel too confident yet, it might redevelop. Where can I get ahold of a new fuel pump and what brand is recommended? The car will remain relatively stockish so no need for an upgrade I would have thought

No one is suggesting you replace the fuel pump.....test it first....or get it tested

rob82 Mentor

rob82

Posted
Posted (edited)

Havn't got a vacuum leak do you? Also is there a throttle switch as well as sensor? No one here has mentioned 02 sensor - which may have been disturbed when you changed the dump pipe.

If its fine under tull throttle its unlikely to be the fuel pump.

Edited by rob82
TUF250 Proficient

TUF250

Posted
  • Author
Posted

I have considered the o2 sensor, im sourcing a new one at the moment but public holiday today which is not helping (i am getting all the casual staff on the phone who have no clue!) vac leak is my next step along with fuel (although its fine up top so i doubt it, however I will test it to be sure)

I was only asking about the fuel pump in case it came to that, was just curious.

TUF250 Proficient

TUF250

Posted
  • Author
Posted

well interestingly the porblem appears to be fixed. I cleaned the acc valve the otehr day and put it all back together and no change which I was really dissapointed with after being sure from what I have read that this was the problem. I took the car back home, reset the ecu and redid the battery earth in the boot as a was not happy with it and it has been fine since, 2 days now so I think I might have got it.

Fingers crossed! thumbs up again to all the guys who helped and A++ to another great DIY thread which helped out heaps!

The Dan Grand Master

The Dan

Posted
Posted
well interestingly the porblem appears to be fixed. I cleaned the acc valve the otehr day and put it all back together and no change which I was really dissapointed with after being sure from what I have read that this was the problem. I took the car back home, reset the ecu and redid the battery earth in the boot as a was not happy with it and it has been fine since, 2 days now so I think I might have got it.

Fingers crossed! thumbs up again to all the guys who helped and A++ to another great DIY thread which helped out heaps!

Re doing the battery earths was a good idea! :blink:

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