Rough idle on warm start up (20 minutes), 87 7MGTE

Bru · 02-04-2011, 02:00 AM

I repeated my test by thoroughly warming up the engine and letting it set shut down for 20 minutes with the hood closed. Then I disconnected the fuel pressure regulator vacuum line and plugged it up. The car started and idled normally for 3 seconds then I shut it off. I immediately reattached the vacuum line and started up again and ran rough as it usually does under these conditions. It occurred to me that I had performed the same function as the High Temp Fuel Pressure Up VSV located under the intake manifold at the front of the engine. I've known for quite some time that mine was bad and did not function which means it allowed vacuum to the regulator under all conditions. They go bad by being electrically open. (no resistance at the terminals). Until now this hasn't mattered but I guess it needs it to prevent vapor lock or 10 pounds more fuel pressure making it 40 PSI for the first minute of hot startup. Here's a very informative web page about fuel systems check out page 16. It details the Toyota high temperature (pressure up) fuel control.

www.autoshop101.com/forms/h42.pdf

02-04-2011, 02:00 AM	#5
Bru Bone Stock w Upgrades ;-) Join Date: Apr 2010 Location: Tampa Bay Posts: 202	I may have this solved. I repeated my test by thoroughly warming up the engine and letting it set shut down for 20 minutes with the hood closed. Then I disconnected the fuel pressure regulator vacuum line and plugged it up. The car started and idled normally for 3 seconds then I shut it off. I immediately reattached the vacuum line and started up again and ran rough as it usually does under these conditions. It occurred to me that I had performed the same function as the High Temp Fuel Pressure Up VSV located under the intake manifold at the front of the engine. I've known for quite some time that mine was bad and did not function which means it allowed vacuum to the regulator under all conditions. They go bad by being electrically open. (no resistance at the terminals). Until now this hasn't mattered but I guess it needs it to prevent vapor lock or 10 pounds more fuel pressure making it 40 PSI for the first minute of hot startup. Here's a very informative web page about fuel systems check out page 16. It details the Toyota high temperature (pressure up) fuel control. www.autoshop101.com/forms/h42.pdf Last edited by Bru; 03-14-2011 at 03:11 AM.