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

sin0186 · 12-13-2014, 12:11 AM

After I accelerate and come out of a gear my rpm drops down all the way about 300rpms then jumps up to 1400rpms then drops back down, see sawing like that until it eventually levels out around 1000rpms, which is a normal idle for my car. Is this vacuum related? Could someone give me an in-depth analysis on the situation and possible tell me how to fix the problem? Thanks in advance.

jza80king · 12-13-2014, 01:55 AM

Quote:

Originally Posted by sin0186

After I accelerate and come out of a gear my rpm drops down all the way about 300rpms then jumps up to 1400rpms then drops back down, see sawing like that until it eventually levels out around 1000rpms, which is a normal idle for my car. Is this vacuum related? Could someone give me an in-depth analysis on the situation and possible tell me how to fix the problem? Thanks in advance.

SR? KA? Have you pulled any codes if so, what codes were you getting? Need more info but just off the top of my head sounds like IAC Valve, Coolant Temp sensor or possibly Throttle Position sensor. Vacuum could be it, I recently rebuilt my KA24DE and the way I found I had several cracked and leaking vacuum lines was I sprayed soapy water from a spray bottle onto my vacuum lines and noticed bubbles from the escaping air, give that a shot.

sin0186 · 12-13-2014, 09:48 AM

It's a SR. I just finished the swap and been having ffew hiccups. Just trying to get this bad boy in optimal condition.

Kingtal0n · 12-14-2014, 05:15 PM

sounds like your blow-off is vented to the atmosphere. The engine goes high vacuum, the bypass opens, the air exits, the maf voltage spikes, the air fuels go rich, the engine bogs, the bypass shuts, the maf voltage goes back to normal, the air fuel goes back to normal, the rpm comes up, the vacuum comes back, the bypass opens again, and repeat.

All of that assumes the ECU is stock. A poorly written timing / fuel map can also do the same thing.

12-13-2014, 12:11 AM	#1
sin0186 Join Date: Nov 2008 Location: Portland OR Posts: 15 Trader Rating: (0) Feedback Score: 0 reviews	RPM Issues. After I accelerate and come out of a gear my rpm drops down all the way about 300rpms then jumps up to 1400rpms then drops back down, see sawing like that until it eventually levels out around 1000rpms, which is a normal idle for my car. Is this vacuum related? Could someone give me an in-depth analysis on the situation and possible tell me how to fix the problem? Thanks in advance.

12-13-2014, 09:48 AM	#3
sin0186 Join Date: Nov 2008 Location: Portland OR Posts: 15 Trader Rating: (0) Feedback Score: 0 reviews	It's a SR. I just finished the swap and been having ffew hiccups. Just trying to get this bad boy in optimal condition.

12-14-2014, 05:15 PM	#4
Kingtal0n Post Whore! Join Date: Jul 2005 Location: South Florida Age: 41 Posts: 4,829 Trader Rating: (17) Feedback Score: 17 reviews	sounds like your blow-off is vented to the atmosphere. The engine goes high vacuum, the bypass opens, the air exits, the maf voltage spikes, the air fuels go rich, the engine bogs, the bypass shuts, the maf voltage goes back to normal, the air fuel goes back to normal, the rpm comes up, the vacuum comes back, the bypass opens again, and repeat. All of that assumes the ECU is stock. A poorly written timing / fuel map can also do the same thing.