c4 rough idle?
Thread Starter
Instructor
Joined: Oct 2005
Posts: 120
Likes: 1
c4 rough idle?
IM some what seasoned with the tpi engine (1991) , but I have a miss in the idle threw low rpm (900- 1,100). I have installed new injectors (stock #), fuel pump, regulator, check for vacum leaks, new plugs/ cap & rotor/ & coil. Any ideas for the new member?
Advanced
Joined: Dec 2004
Posts: 66
Likes: 0
From: Kansas City Missouri
Originally Posted by CMYC4
IM some what seasoned with the tpi engine (1991) , but I have a miss in the idle threw low rpm (900- 1,100). I have installed new injectors (stock #), fuel pump, regulator, check for vacum leaks, new plugs/ cap & rotor/ & coil. Any ideas for the new member?
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Is your TPS set correctly? Have you tried slighty adjusting it to make the computer think your throttle is further open? If not, give that a go, it might help. It cant hurt anyway. If you have thrown all that new stuff at it and still no joy there is not much left apart from that and dirty/mal-adjusted IAC and or throttle plates as stated by Rtremain. Also check the MAP sensor for cleanliness.
Melting Slicks
Joined: Jan 2001
Posts: 2,940
Likes: 5
From: Chesapeake VA
From the parts you have listed as being replaced, it seems like you have covered most of the fuel and spark areas. I would look into the air department; any vacuum leaks, clean throttle body, etc. I would also check the timing, setting that to stock can smooth your idle out a little.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
With all that's you've checked or replaced, I'd take a compression check hot and cold and look closely at #7 for signs of a leaking head gasket. Compare the plug to the others and look for rust on the threads.
Burning Brakes
Joined: Oct 2005
Posts: 866
Likes: 4
From: Iowa
I had a rough idle when I recently purchased my 89 w/ L98. Took it a friend who hooked it up to an analyzier ----- needed new O2 sensor. Put in a new sensor and fuel filter at the same time -------- idles smoothly now and took out the low end acceleration hesitation out.
Advanced
Joined: Nov 2005
Posts: 54
Likes: 1
From: San Jose California
I noticed you didn't mention spark plug wires; if not routed properly they like to lean on the exhaust manifolds and either burn or wear down from the heat. Double check those closely and pay special attention to the boots on the plug wires, they tend to deteriorate and not make a proper contact. Also try spraying your spark plug wires with water via a plastic spray bottle, if one of your wires has a bare spot it will arc and help you pinpoint the problem.
Have you checked your timing? Off the top of my head I think it should be 6* BTDC for your vehicle, but don't quote me on that setting though, the actual timing setting is on your emissions tag under your hood.
Let us know what your find out and good luck ...
Have you checked your timing? Off the top of my head I think it should be 6* BTDC for your vehicle, but don't quote me on that setting though, the actual timing setting is on your emissions tag under your hood.
Let us know what your find out and good luck ...
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Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Originally Posted by VetBoy89II
I noticed you didn't mention spark plug wires; if not routed properly they like to lean on the exhaust manifolds and either burn or wear down from the heat. Double check those closely and pay special attention to the boots on the plug wires, they tend to deteriorate and not make a proper contact. Also try spraying your spark plug wires with water via a plastic spray bottle, if one of your wires has a bare spot it will arc and help you pinpoint the problem.
Have you checked your timing? Off the top of my head I think it should be 6* BTDC for your vehicle, but don't quote me on that setting though, the actual timing setting is on your emissions tag under your hood.
Let us know what your find out and good luck ...
Have you checked your timing? Off the top of my head I think it should be 6* BTDC for your vehicle, but don't quote me on that setting though, the actual timing setting is on your emissions tag under your hood.
Let us know what your find out and good luck ...
Did you also notice the problem is between 900-1,100 rpm?? If the leads are that bad id be inclined to think they would cause issue higher up in RPM also,but then you may be right too. I reckon try a slight advance on youre TPS (thats the Thottle Position Sensor,located on the right hand side of the throttle body) you have nothing to lose by giving this a go, and at the same time, get some throttle body cleaner spray, and clean the throttle body including the IAC intake hole. Are there any diagnostic codes logged in the system at all?
Thread Starter
Instructor
Joined: Oct 2005
Posts: 120
Likes: 1
OK< problem solved! Apparently some joker at the part store had open up a spark plug box and put (1) iron head plug in a pac of 8 aluminum plugs! Well as IM sure you all know, the iron head plug has a much shorter shorter thread depth than an aluminum plug. In a nut shell, it causes your car to idle a little funny. No harm done but My fault, I should of seen it when I was gappin, but it was a late night ya know :-) Thanks guy's...... JC
Le Mans Master
Joined: May 2005
Posts: 5,214
Likes: 65
From: Queensland, AUSTRALIA
Originally Posted by CMYC4
OK< problem solved! Apparently some joker at the part store had open up a spark plug box and put (1) iron head plug in a pac of 8 aluminum plugs! Well as IM sure you all know, the iron head plug has a much shorter shorter thread depth than an aluminum plug. In a nut shell, it causes your car to idle a little funny. No harm done but My fault, I should of seen it when I was gappin, but it was a late night ya know :-) Thanks guy's...... JC
