hunting idle - no codes
Thread Starter
Heel & Toe
Joined: May 2006
Posts: 21
Likes: 0
From: Pittsburgh Pennsylvania
hunting idle - no codes
I started my 89 recently and after entering closed loop the idle starts to drop slightly and pick back up. It seems to be doing this in a cycle of down and back. Almost sounds like it wants to stall and catches itself and picks back up. No problems when revved. I recently replaced the injectors, fuel pump, iac, cleaned throttle body. Soon as the coolant temp registers idle starts fluctuating. Have not changed the TPS, coolant temp sensor, o2, or plugs yet. Fuel pressure is good. Anyone have any other ideas of what might cause this? Thanks.
Navigator
Joined: Apr 2006
Posts: 9
Likes: 0
Have you double checked the voltage at the TPS?
Did the IAC get seated properly on install?
Is the base timing and throttle opening set? ( see TPS)
if no problem when revved what is the fuel pressure at idle compared to when vaccum applied to regulator?
are all the injectors seated and working?
Did the IAC get seated properly on install?
Is the base timing and throttle opening set? ( see TPS)
if no problem when revved what is the fuel pressure at idle compared to when vaccum applied to regulator?
are all the injectors seated and working?
Advanced
Joined: May 2010
Posts: 89
Likes: 0
From: Morgans Point Resort Texas
vac leak
sounds very much like a vacuum leak. I have a 93 GMC that did exactly that and it was a broken vacuum hose. I was fortunate to have a friend who had a smoke machine, and found the broken connector behind engine.
Racer
Joined: Sep 2001
Posts: 266
Likes: 7
From: Sumner WA
I agree with the vacuum leak. If you put a data logger on it I bet you'll see your IAC moving a lot. Heres a screen shot of mine when it was doing the same; the line going all over the place is the IAC position:
Advanced
Joined: Jun 2010
Posts: 72
Likes: 0
I'd like to piggy back off of this thread if you don't mind. I guess you could say I'm new to the Vette scene, considering I've owned my '93 for a grand total of 2 DAYS!! I haven't even registered it yet!
Now on to the problem: Same as stated above, the idle is all over the place. I'll start looking for vacuum leaks tonight. However, a new caviot to add to this; last night, driving home in moderate traffic (moving around 50 - 65 but variable), it start bucking and hesitating when it would load up a bit. If I pulled it back a gear so the RPM's were up a little higher, it didn't do it. If I just nail it, it's fine... Does this sound like time to clean the injectors? Before I just dive in, I figured I'd consult with any of y'all who could provide some experienced feedback... Thanks in advance!
Now on to the problem: Same as stated above, the idle is all over the place. I'll start looking for vacuum leaks tonight. However, a new caviot to add to this; last night, driving home in moderate traffic (moving around 50 - 65 but variable), it start bucking and hesitating when it would load up a bit. If I pulled it back a gear so the RPM's were up a little higher, it didn't do it. If I just nail it, it's fine... Does this sound like time to clean the injectors? Before I just dive in, I figured I'd consult with any of y'all who could provide some experienced feedback... Thanks in advance!
Former Vendor
Joined: Nov 2006
Posts: 2,482
Likes: 3
From: Carmichael ca
I'd like to piggy back off of this thread if you don't mind. I guess you could say I'm new to the Vette scene, considering I've owned my '93 for a grand total of 2 DAYS!! I haven't even registered it yet!
Now on to the problem: Same as stated above, the idle is all over the place. I'll start looking for vacuum leaks tonight. However, a new caviot to add to this; last night, driving home in moderate traffic (moving around 50 - 65 but variable), it start bucking and hesitating when it would load up a bit. If I pulled it back a gear so the RPM's were up a little higher, it didn't do it. If I just nail it, it's fine... Does this sound like time to clean the injectors? Before I just dive in, I figured I'd consult with any of y'all who could provide some experienced feedback... Thanks in advance!
Now on to the problem: Same as stated above, the idle is all over the place. I'll start looking for vacuum leaks tonight. However, a new caviot to add to this; last night, driving home in moderate traffic (moving around 50 - 65 but variable), it start bucking and hesitating when it would load up a bit. If I pulled it back a gear so the RPM's were up a little higher, it didn't do it. If I just nail it, it's fine... Does this sound like time to clean the injectors? Before I just dive in, I figured I'd consult with any of y'all who could provide some experienced feedback... Thanks in advance!
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Melting Slicks
Joined: Sep 2008
Posts: 2,376
Likes: 111
From: Cherokee National Forest TN
All vacuum hoses & connections.
Mine recently had the same running symptoms, found the problem when I pulled a vacuum on the brake booster. It would only pull 10" of vacuum with my AC vacuum pump & drop to zero the moment I closed the valve. Replaced the booster, motor is happy.
Mine recently had the same running symptoms, found the problem when I pulled a vacuum on the brake booster. It would only pull 10" of vacuum with my AC vacuum pump & drop to zero the moment I closed the valve. Replaced the booster, motor is happy.
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
It may be because of the vacuam leak but your car was running Pig rich..The long and short term fuel readings should of set a code being that rich..WW
