Captain C

When I first fire the car up it has a bad surging problem. It has wild throttle swings that get so bad that it shuts the car down. That goes away for the most part once the car is warmed up.

I changed out the IAC and it still has the same problem. Hopefully my stuff from Craig Moates arrives this week (shipped out Friday) so I can hook my laptop up to the computer and check it out. I'm probably going to reinstall my 165 computer because it will give me readings faster.

Since this was happening before I changed to the larger injectors, I don't think that had anything to do with it. The only other thing that has changed on the car recently is the harmonic balancer. I had to switch to the 7.25" Fluidamper from the 6.25" Fluidamper due to the heavier pistons that were put into the engine during the last rebuild. That eliminated that pesky miss that would normally be identified as a slipped outer ring on a standard harmonic balancer. The car runs much smoother now and I can't imagine the new balancer causing this problem.

I have run this cam for 5 or 6 years and this model computer (870) for a large portion of those years as well. This particular ECM only has about 6 months of run time since it was remanufactured.

Anybody with any ideas on things to look for????

dyeager535

I had a similar problem with wild swings of RPM at idle (especially cold) but I had a few other things going on. (bad MAF esp.)

Anyways, I did notice one thing that wasn't the problem, but made it worse...if the fan was on, when the idle swung low, the alternator load was too much, and would kill the motor. Unplug the fan, and the RPM's would still swing, but not as much, and not enough to kill the engine.

Of course this was due to the bad MAF, which was throwing a code, which was forcing the fan to run 24-7. (not that it matters in this case, but once the MAF was replaced, idle fluctuation disappeared and the fan worked correctly)

I know, kind of an "out there" issue, but I figured I'd mention it.

Captain C

I have a brand new MAF, but I may have oiled my air filters. I can clean any oil off of the inside of the MAF with electrical contact cleaner, but usually it throws a code when that happens and it's not throwing a code.

I might need to check my knock sensor to see if it's any good. I was getting that same kind of thing happening at mid range conditions and my knock sensor bypass switch was in the bypass mode. Something I never do without 100 octane in the tank..... I need to just rip out the switch anyway! If it was the problem now you would think that the throttle swings would be happening throughout the entire RPM band and it's not.

Thanks for the idea though. I'll definitley check it out!!!!

formula_novice

iTrader: (1)

I have had idle problems with my car also.
I have found that common causes are the IAC, fuel injectors, vacuum leaks, or a failing fuel pump.

Hope this helps.

Captain C

I have a new IAC, brand spanking new 30# injectors (but started doing it with the 24# units that I ran for 50k miles just before I did the swap), I have no vacuum leaks and I will check the fuel pump.

While I question teh fuel pumps output being large enough (Buick GN pump), you would think with steady fuel pressure it would idle fine. I disconnected the vacuum line to the fuel pump to see if it made any difference and it didn't. I guess I need to check the voltage to the relay to make sure it's not that. The engine was hot at the time so I didn't want to connect my gauge. Hopefully Friday evening I can look at it. Way too much going on between now and then.

dyeager535

I don't think I'd worry too much about the voltage to the fuel pump relay.

I *really* doubt your engine would even run if the fuel pump wasn't seeing voltage all the time. Not to mention, clearing up once the car is warm would also point away from that.

It certainly seems to point to something that is affected by engine temperature.