RB25DET Idle Issues - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

encludemeout · 03-10-2012, 04:36 PM

Here is the background on my car. S13 with an S1 RB25DET swap.

Freddy Intake w/ Q45 throttle body
Z32 Fuel Filter
Walbro 255
FMIC
Full 3 Inch Exhaust
Stock Boost
Stock ECU
Stock MAF
Greddy Type S BOV, vented

Since I got my swap running, idle has always been an issue with it. On a cold start, it will sit anywhere from 1500-1600 rpm's. Then once warm drops down to anywhere from 800-1000 rpm's. That all seems normal. These are the issues I'm having with it.

-When rolling, if the car is put into neutral it will immediately jump up to around 500 rpms HIGHER than normal. So if it's still in cold start mode, it'll be around 2000 rpm, and if warmed up around 1300-1500 rpm. This will sit up around there until I come to a complete stop. Then as soon as I'm stopped, it drops to it's usual position.

-I can get almost no adjustment out of the idle screw. I did it the correct way, by letting the car warm up to operating temp, unplugging the tps sensor and adjusting the idle screw. Hardly any noticeable adjustment. Last time I check is was getting power too. I cleaned it out today and still not luck.

-Every now and then I'll get the classic Honda idle for a ~15 seconds. It goes up and down within around a 700 rpm range.

-If free rev'd above 4500 rpm's the motor wont be able to catch itself, and it dies. It will start right back up though.

-If you are rolling and punch it, the car will stutter initially and then go. Boost's fine and everything, it just seems as if it needs a split second to get it's shit together.

I'm about to buy a new IAC valve and see if it makes any difference. I currently have a three bolt valve, and need to find a replacement for it if anyone knows. Some say a 1.6L 91-94 Sentra will work, but after looking at pictures it doesn't look even remotely the same. Car runs really good besides all this. Anyone think IAC with me, or maybe a possible vacuum leak?

Sileighty_85 · 03-10-2012, 04:40 PM

Check timing, vac/boost leaks, clean MAFS

Frank_Jaeger · 03-10-2012, 04:59 PM

Given the symptoms I'd say it's likely to be either the IACV or a vac leak. Possibly a vac leak on the IACV lol. I have the same exact symptoms, and I got a vac leak on the IM, somewhere around the EGR. I've a KA though.

encludemeout · 03-10-2012, 05:38 PM

Timing has always been dead on, and I have cleaned the MAFS and it is good I'd say. No rips or tears in the screens and it looks clean. I could possibly try a different one. I think I'm about to bite the bullet on an IACV. Anyone have a part number for one that's available here in the states?

Sileighty_85 · 03-10-2012, 05:55 PM

NissanParts.cc - Your #1 Source for OEM Parts and Accessories

Frank_Jaeger · 03-10-2012, 06:57 PM

I'd go to town with starter fluid first before buying an IACV.

03-10-2012, 04:40 PM	#2
Sileighty_85 Post Whore! Join Date: Dec 2006 Location: Misawa, Japan Posts: 6,815 Trader Rating: (8) Feedback Score: 8 reviews	Check timing, vac/boost leaks, clean MAFS __________________ 後輪駆動車１番 1989 Built SR GT2871R -363whp 1998 S14 W/RB25- 250ish (For Now) 1986 SR86 - 200ish 1990 R32 GTR - 320hp Don't Buy Engines from JDM-Online http://zilvia.net/f/businesses/207457-jdm-online.html Don't Buy XS-Power or SSAC Shit

03-10-2012, 05:55 PM	#5
Sileighty_85 Post Whore! Join Date: Dec 2006 Location: Misawa, Japan Posts: 6,815 Trader Rating: (8) Feedback Score: 8 reviews	NissanParts.cc - Your #1 Source for OEM Parts and Accessories __________________ 後輪駆動車１番 1989 Built SR GT2871R -363whp 1998 S14 W/RB25- 250ish (For Now) 1986 SR86 - 200ish 1990 R32 GTR - 320hp Don't Buy Engines from JDM-Online http://zilvia.net/f/businesses/207457-jdm-online.html Don't Buy XS-Power or SSAC Shit

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03-10-2012, 04:36 PM	#1
encludemeout Zilvia Member Join Date: Jul 2008 Location: Ohio Posts: 224 Trader Rating: (7) Feedback Score: 7 reviews	RB25DET Idle Issues Here is the background on my car. S13 with an S1 RB25DET swap. Freddy Intake w/ Q45 throttle body Z32 Fuel Filter Walbro 255 FMIC Full 3 Inch Exhaust Stock Boost Stock ECU Stock MAF Greddy Type S BOV, vented Since I got my swap running, idle has always been an issue with it. On a cold start, it will sit anywhere from 1500-1600 rpm's. Then once warm drops down to anywhere from 800-1000 rpm's. That all seems normal. These are the issues I'm having with it. -When rolling, if the car is put into neutral it will immediately jump up to around 500 rpms HIGHER than normal. So if it's still in cold start mode, it'll be around 2000 rpm, and if warmed up around 1300-1500 rpm. This will sit up around there until I come to a complete stop. Then as soon as I'm stopped, it drops to it's usual position. -I can get almost no adjustment out of the idle screw. I did it the correct way, by letting the car warm up to operating temp, unplugging the tps sensor and adjusting the idle screw. Hardly any noticeable adjustment. Last time I check is was getting power too. I cleaned it out today and still not luck. -Every now and then I'll get the classic Honda idle for a ~15 seconds. It goes up and down within around a 700 rpm range. -If free rev'd above 4500 rpm's the motor wont be able to catch itself, and it dies. It will start right back up though. -If you are rolling and punch it, the car will stutter initially and then go. Boost's fine and everything, it just seems as if it needs a split second to get it's shit together. I'm about to buy a new IAC valve and see if it makes any difference. I currently have a three bolt valve, and need to find a replacement for it if anyone knows. Some say a 1.6L 91-94 Sentra will work, but after looking at pictures it doesn't look even remotely the same. Car runs really good besides all this. Anyone think IAC with me, or maybe a possible vacuum leak?

03-10-2012, 04:59 PM	#3
Frank_Jaeger Zilvia FREAK! Join Date: Jan 2012 Location: Port Charlotte, Florida Age: 33 Posts: 1,352 Trader Rating: (1) Feedback Score: 1 reviews	Given the symptoms I'd say it's likely to be either the IACV or a vac leak. Possibly a vac leak on the IACV lol. I have the same exact symptoms, and I got a vac leak on the IM, somewhere around the EGR. I've a KA though.

03-10-2012, 05:38 PM	#4
encludemeout Zilvia Member Join Date: Jul 2008 Location: Ohio Posts: 224 Trader Rating: (7) Feedback Score: 7 reviews	Timing has always been dead on, and I have cleaned the MAFS and it is good I'd say. No rips or tears in the screens and it looks clean. I could possibly try a different one. I think I'm about to bite the bullet on an IACV. Anyone have a part number for one that's available here in the states?

03-10-2012, 06:57 PM	#6
Frank_Jaeger Zilvia FREAK! Join Date: Jan 2012 Location: Port Charlotte, Florida Age: 33 Posts: 1,352 Trader Rating: (1) Feedback Score: 1 reviews	I'd go to town with starter fluid first before buying an IACV.