RB25det idling/acceleration issue.. please help !!

6090 Views 8 Replies 4 Participants Last post by Adz1282, Oct 9, 2015

lexik17

Discussion Starter · Oct 2, 2015

hey guys, new to skylines ! imported my 93 R32 GTST, RB25det swap in June. Has been running great up until about 2 weeks ago. I have been searching and searching and talking to many people and I can't seem to get this issue straightened out ...

These issues were only occurring randomly, didn't matter whether the engine was cold or hot. Sometimes at idle, the rpms will jump up and down, eventually the car will die unless I feather the gas constantly. Also, when driving on occasion in low gears up to third, it will hesitate and stutter when I try to give it gas and eventually catch. On one of the worst occasions, I had the pedal to the floor and the car wouldn't move for a good 3 seconds and then it would catch and lurch forward. The problem seeeeems to be getting increasingly worse but its hard to say...

Here are the things I have tried :

- Coil packs
- Fuel pump
- Spark plugs
- Fuel Filter
- Ignitor chip
- Fixed some cracked hose
- Checked for vacuum leaks
- Cleaned/replaced MAF
- Cleaned IACV

All of this lead to me thinking that my TPS was bad .... Well upon trying to adjust my TPS , I can't get the signal wire to read lower than .8 V ... and its supposed to be somewhere around .5 V I believe. But, when I put my boyfriends TPS off his car onto mine, it was doing the same thing where as on his car, it was adjusting fine. Which THEN lead me to believe my TPS wasnt actually messed up, because if I take my TPS off the throttle body, I can fully adjust the TPS to where it needs to be .... So with my TPS adjusted to the lowest it can go ( .8V ), when I start the car up it idles at 2000 rpm.

SO, I decided to check codes on my ECU ... I got 34 knock sensor and 21 ignition circuit ( but I think the 21 just meant that my battery is dying since I've had the ignition on and not started the car for a while )

ALSOOOOO, today we noticed that my coolant is foaming D:

My BOV is not atmospheric.

Can anyoneeeee please give me some insight ??? Maybe this is a plethora of problems ... wondering why they all popped up at the same time

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goldtooth

· #2 · Oct 2, 2015

On my R34 code 21 was coilpacks. Not sure if R32 is the same but search forum for that code. One turned out to be intermittently breaking down and caused rough running at idle and through the revs.

Sent from my XT1072 using Tapatalk

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Tricky-Ricky

· #3 · Oct 2, 2015 (Edited)

First thing I would check is the cold start valve located under the plenum, they fail open so you get high idle due to this, if you locate the rubber pipe as it returns to the plenum, you can pinch with a pair of pliers, if the idle drops considerably, you have found your problem.
Not too sure about the TPS voltage, but it may be related to the high idle, check the cold start first.

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lexik17

Discussion Starter · #4 · Oct 2, 2015

goldtooth said:
On my R34 code 21 was coilpacks. Not sure if R32 is the same but search forum for that code. One turned out to be intermittently breaking down and caused rough running at idle and through the revs.

Sent from my XT1072 using Tapatalk

i think on the rb25 ecu the 21 code is ignition circuit .. we swapped in my boyfriends coil packs which we know are in good working order and it didnt seem to change anything

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lexik17

Discussion Starter · #5 · Oct 2, 2015

Tricky-Ricky said:
First thing I would check is the cold start valve located under the plenum, they fail open so you get high idle due to this, if you locate the rubber pipe as it returns to the plenum, you can pinch with a pair of pliers, if the idle drops considerably, you have found your problem.
Not too sure about the TPS voltage, but it may be related to the high idle, check the cold start first.

is this located near the IACV ..? I noticed there is a purple plug there which has nothing plugged into it ... i think the brown one next to it is the IACV plug ?

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Tricky-Ricky

· #6 · Oct 2, 2015

Have a look at the pics in this thread, it should help you identify the parts.

http://www.skylineowners.com/forum/13- general/196650-cold-start-valve-location-help-2.html

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Adz1282

· #7 · Oct 5, 2015

''ALSOOOOO, today we noticed that my coolant is foaming D:''

Looks to me like your head gasket has gone! Probably lost compression causing your problems.

If your expansion tank is still pressurised when cold then you need to sort your head gasket out. It will be leaking from the cylinder to the coolant channels.

Luckily compared to newer cars the RB is fairly straight forward to get the head off.

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lexik17

Discussion Starter · #8 · Oct 9, 2015

Adz1282 said:
''ALSOOOOO, today we noticed that my coolant is foaming D:''

Looks to me like your head gasket has gone! Probably lost compression causing your problems.

If your expansion tank is still pressurised when cold then you need to sort your head gasket out. It will be leaking from the cylinder to the coolant channels.

Luckily compared to newer cars the RB is fairly straight forward to get the head off.

Don't think it's my head gasket because my car has never overheated nor is there coolant in my oil or vice versa .... Thinking it may just need a coolant flush since it still has the coolant in their from when it was in Japan, might just be old ...? But will do a compression test anyways to be sure

Got under the car today and found a wire broken off from my knock sensor ... Most likely the cause of the ecu code ... Also cleaned my TB which was very dirty and now am able to adjust my TPS properly

things are looking up! May get one last ride out of it before I put him away for the winter

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Adz1282

· #9 · Oct 9, 2015

Just check the coolant expansion tank is not pressurised when cold. Head gasket failures have many different symptoms depending on what parts of the gasket has failed.

If it has gone between the piston cylinder and the water channel it is possible for the high pressure in the piston cylinder to leak through to the water/coolant. But does not always leak back as it in now at much lower pressure. It shows as foamed coolant and pressurised coolant system even at ambient temp.

Not trying to scare you, just wouldn't want it to get any worse without at least checking it out.

Good luck and I hope it turns out to be a simple fix.

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