Erratic idle?

Dezmond121 · 04-14-2008, 03:32 PM

Hi, feel a bit stupid posting this problem on the forum as i'm sure this is a very common issue that gets mentioned all the time but have looked at previous threads and none seem to have exactly the same symptoms as my mr2.

Idle speed seems quite high at around 2300rpm on a warm day and close to 3000rpm on a cold day. When it has just been started the idle speed doesnt bounce.

As soon as clutch is dipped when being driven the idle speed rises to about 2200rpm and then falls to about 1500rpm continuously. This can be extremely embarassing when sat at traffic lights as people generally think i want to race them lol.

When normal operating temp is reached the idle speed continues to bounce between the rev range stated above, however, ocassionally (generally when car has been driven for a while (30mins +) the idle speed will remain constant when clutch is dipped at around 1500rpm.

Once warmed up though the idle will remain constant at 1500rpm when the ignition is switched off and then back on again.

Will try adjusting idle air screw tomorrow and check vaccum hoses for any leaks but any suggestions would be muchly appreciated.

lsgheero · 04-14-2008, 06:24 PM

thus far your on the right track check the idle screw and look for possible air leak (might only get present when hoses warm up and expand rubber). Other then that iac (idle air control valve) could need cleaning.

VTsuckah131 · 04-16-2008, 09:24 PM

More often than not in our cars, idling issues can be traced to coolant. You may have an air bubble.

GINA2MR2 · 04-22-2008, 07:06 PM

or tb sensor.. unplug and see if it goes away

Gairloch · 04-22-2008, 09:29 PM

Unfortunately there are tons of possible causes for high idle. What you're describing goes well beyond the typical though at 2-3krpm.

I suspect that you've got a nifty neato air leak in there somewhere. Easiest way to check for leaks in the vacuum lines is to wave an unlit propane torch over them. If you find a leak the engine will rev. You can do the same thing with brake cleaner but I hate spraying that stuff on rubber parts.

If that doesn't yield anything take the intake piping off and inspect the butterfly valve in the throttle body. It could be damaged or there could be something preventing it from closing all the way. Inspect the throttle stop too to make sure it's allowing the valve to close far enough. It should be pretty tight but not actually touching the TB. The copper butterfly valve will actually dig into the aluminum neck of the TB.

If that doesn't work then while you have the intake piping off block the little hole in front of the butterfly valve. That's the ISCV (intake speed control valve) and if it's not functioning correctly can cause high idle. If you block it the idle speed should drop like it's going to stall. If it doesn't then you will want to disassemble it and clean it out thoroughly with brake cleaner.

nd4mr2spd · 07-30-2008, 02:13 AM

Quote:

Originally Posted by Gairloch

Unfortunately there are tons of possible causes for high idle. What you're describing goes well beyond the typical though at 2-3krpm.

I suspect that you've got a nifty neato air leak in there somewhere. Easiest way to check for leaks in the vacuum lines is to wave an unlit propane torch over them. If you find a leak the engine will rev. You can do the same thing with brake cleaner but I hate spraying that stuff on rubber parts.

If that doesn't yield anything take the intake piping off and inspect the butterfly valve in the throttle body. It could be damaged or there could be something preventing it from closing all the way. Inspect the throttle stop too to make sure it's allowing the valve to close far enough. It should be pretty tight but not actually touching the TB. The copper butterfly valve will actually dig into the aluminum neck of the TB.

If that doesn't work then while you have the intake piping off block the little hole in front of the butterfly valve. That's the ISCV (intake speed control valve) and if it's not functioning correctly can cause high idle. If you block it the idle speed should drop like it's going to stall. If it doesn't then you will want to disassemble it and clean it out thoroughly with brake cleaner.

I like your iac test - mine specs out but I still am not convinced that it's working properly

04-14-2008, 03:32 PM	#1 (permalink)
Dezmond121 No Skills Join Date: Apr 2008 Posts: 1 Thanks: 1 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	Erratic idle? Hi, feel a bit stupid posting this problem on the forum as i'm sure this is a very common issue that gets mentioned all the time but have looked at previous threads and none seem to have exactly the same symptoms as my mr2. Idle speed seems quite high at around 2300rpm on a warm day and close to 3000rpm on a cold day. When it has just been started the idle speed doesnt bounce. As soon as clutch is dipped when being driven the idle speed rises to about 2200rpm and then falls to about 1500rpm continuously. This can be extremely embarassing when sat at traffic lights as people generally think i want to race them lol. When normal operating temp is reached the idle speed continues to bounce between the rev range stated above, however, ocassionally (generally when car has been driven for a while (30mins +) the idle speed will remain constant when clutch is dipped at around 1500rpm. Once warmed up though the idle will remain constant at 1500rpm when the ignition is switched off and then back on again. Will try adjusting idle air screw tomorrow and check vaccum hoses for any leaks but any suggestions would be muchly appreciated.

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04-14-2008, 06:24 PM	#2 (permalink)
lsgheero RAR! Join Date: Feb 2007 Location: Arizona Posts: 747 Thanks: 9 Thanked 31 Times in 31 Posts My Google Map iTrader Rating: (1/100% )	thus far your on the right track check the idle screw and look for possible air leak (might only get present when hoses warm up and expand rubber). Other then that iac (idle air control valve) could need cleaning.

04-16-2008, 09:24 PM	#3 (permalink)
VTsuckah131 Sirc's secret lover Join Date: Feb 2006 Location: Northern VA Posts: 514 Thanks: 0 Thanked 13 Times in 12 Posts iTrader Rating: (1/100% )	More often than not in our cars, idling issues can be traced to coolant. You may have an air bubble.

04-22-2008, 07:06 PM	#4 (permalink)
GINA2MR2 Not A VR6 Join Date: Dec 2007 Location: J-Town Posts: 339 Thanks: 3 Thanked 7 Times in 7 Posts iTrader Rating: (0/0% )	or tb sensor.. unplug and see if it goes away

04-22-2008, 09:29 PM	#5 (permalink)
Gairloch Dreaming of apexes Join Date: Aug 2005 Location: Minneapolis, MN Posts: 5,313 Thanks: 139 Thanked 296 Times in 264 Posts Blog Entries: 4 My Google Map iTrader Rating: (7/100% )	Unfortunately there are tons of possible causes for high idle. What you're describing goes well beyond the typical though at 2-3krpm. I suspect that you've got a nifty neato air leak in there somewhere. Easiest way to check for leaks in the vacuum lines is to wave an unlit propane torch over them. If you find a leak the engine will rev. You can do the same thing with brake cleaner but I hate spraying that stuff on rubber parts. If that doesn't yield anything take the intake piping off and inspect the butterfly valve in the throttle body. It could be damaged or there could be something preventing it from closing all the way. Inspect the throttle stop too to make sure it's allowing the valve to close far enough. It should be pretty tight but not actually touching the TB. The copper butterfly valve will actually dig into the aluminum neck of the TB. If that doesn't work then while you have the intake piping off block the little hole in front of the butterfly valve. That's the ISCV (intake speed control valve) and if it's not functioning correctly can cause high idle. If you block it the idle speed should drop like it's going to stall. If it doesn't then you will want to disassemble it and clean it out thoroughly with brake cleaner.