LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Rpm problems

Thread Tools
 
Search this Thread
 
Old Oct 31, 2014 | 03:50 PM
  #1  
Black93lt1's Avatar
Thread Starter
Registered User
 
Joined: Jul 2013
Posts: 83
Rpm problems

I have a 93 lt1 that normally idles at 1k rpms and right now it is jumping up to 2k and 1.5k at idle it will also drop down to 500 and try to die....what's wrong???
Old Oct 31, 2014 | 04:29 PM
  #2  
Injuneer's Avatar
Administrator
 
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
Re: Rpm problems

Manual or auto trans? RPM is controlled by the ECM (computer). Stock for the M6 is 800 RPM, stock for the A4 is 550 RPM in gear and 650 RPM in neutral. The tach typically seems to read 100-200 RPM higher than actual engine speed. That is based on a fully warmed up engine.

I'd start by scanning ot for codes:

http://shbox.com/1/dlc2.jpg

Then check for vacuum leaks.

ECM controls the idle by moving the idle air control valve in the base of the throttle body. It would be interesting to see how the ECM IAC "counts" respond to the high and low idle. You can scan the ECM with TTS Datamaster.... free download, 20 free uses before it asks you to buy a license.

TTS Power Systems
Old Oct 31, 2014 | 04:36 PM
  #3  
Black93lt1's Avatar
Thread Starter
Registered User
 
Joined: Jul 2013
Posts: 83
Re: Rpm problems

I was reading up in different places and one brought up the IAT sensor and be4 after replacing the distributor I started her up with out the air intake attached and she idled great but was really rich and when I did it be4 I had attached the sensor and figured I would check it out so I took the sensor off and now idles great but is running really rich
Old Oct 31, 2014 | 09:22 PM
  #4  
Injuneer's Avatar
Administrator
 
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
Re: Rpm problems

Your 93 uses "speed-density" to calculate the air flow into the engine. It needs an accurate air temperature to make the calculation. Did you disconnect the IAT sensor? If so, it reads an infinite resistance which means a very low temperature = very dense air. That will cause the engine to run rich. It should also set a code.
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Cam's maro
LT1 Based Engine Tech
23
Mar 24, 2015 08:09 PM
edman
General 1967-2002 F-Body Tech
6
Mar 13, 2015 09:39 PM
DetroitZ28
LT1 Based Engine Tech
3
Feb 13, 2015 07:33 AM
edman
General 1967-2002 F-Body Tech
3
Jan 25, 2015 02:41 PM
97SSdude
LT1 Based Engine Tech
9
Dec 31, 2014 07:43 PM




All times are GMT -5. The time now is 07:28 AM.