Engine surges at idle when cold

[jeff1234]

OK, I have chased this thing as far as I can so I will come to you for help. My Charger has a problem with cold idle. It runs the rpm up and then drops off, at times to the point of the engine shutting off. After about three or four minutes of this the span of rpm swings get smaller and smaller and finally the idle settles down to a steady rate. I first suspected a bad AIS, changed it, no help. Changed the TPS, no help. Went through the recommended method of resetting the AIS and idle, no help. So... I bought a OTC 4000E and ran it through the process. No codes, O2 is .5VDC at idle. coolant temp sensor working properly, 12 degree's advance. I checked for vacuum leaks at pcv, bov and all connections and looked through the forum for something similar, no luck. This is a stock CSX cal, stock 89 cam. The OTC 4000 says I am lean at cold idle my AEM seems to concur. After the engine is warm the OTC 4000 says the mixture is rich, the AEM doesn't agree. The engine acts like the AIS is cycling back and forth trying to accommodate a temporary rich condition so I turned my fuel pressure down to 50 PSI, this resulted in a rich/lean lamp cycle on the 4000. Does this sound familiar to anyone?

[going4speed]

Sort of like this idle in the below link? I never did figure it out and it just went away so in to this to see what the outcome is.

[jeff1234]

Yes, that is very nearly the same for all practical purposes. Must be ghosts in the computer. I thought of one more thing to check. I have been doing body work and I have the right side headlight harness ground not connected. I don't see how that could be involved but I will ground it tomorrow and see if that changes anything. If it does I will post.

[going4speed]

One thing that did not set a code for the longest time but that I had suspected, due to stalling issues etc, was the vehicle speed sensor. Since replacing that I have not seen this problem come back.

[raccoon]

did you clean the passage way for the AIS when it was out? gotta be a vacuum leak.

[jeff1234]

Raccoon, I haven't cleaned it recently, but it is worth a try. As pertains to the speed sensor, I have replaced the speed sensor once because of code 15's. it really didn't change anything and I believe that both speed sensors are good.

[jeff1234]

Today I tried some more changes. #1. I reattached the wiring ground, no help. #2. I tried a number of different cam gear changes. Aligning the marks in the middle of the scale made a difference but still not right. #3. I removed the AIS and cleaned the pintle and seat. Got a lot of carbon out of it, This seemed to do the trick. It is still surging slightly from 1100 to 1500 rpms but after about a minute or so it settled right down and acted normal. Warm idle is 12 -13:1 A/F so it is rich. I have my fuel pressure at 50 psi. It is supposed to be 55 psi ??? The injectors are old from an original T-1 Dodge van, I suppose it is possible that one might be leaking. For tomorrow I may try resetting base idle again.
Jeff

[going4speed]

did you ever get this resolved?

[jeff1234]

First of all my apology for taking so long to reply. I was in Florida visiting my daughter. That being said, I removed the 52mm throttle body and spacer and reinstalled the stock 46mm. I reviewed my fuel pressure using a professional quality gauge ( harbor freight stuff is junk, mine was 10 psi low) The other thing I did was try all of my TPS units. I found the one that had the best idle F/A and then tried moving it around within the bounds of he mounting screws to get t best F/A that I could at idle. That seemed to help and it got better from additional starts that I did. When I returned from Florida I started it again in much colder weather than I had before and it idled normally. So while somewhat mysterious in the end I think it had a lot to do with the resistance being sent to the L/M by the TPS and to a lesser degree the larger throttle body.

[going4speed]

The tps is adjustable? I dont think mine is.

[black86glhs]

I had mine do that for the first yr I had it running. Sometimes it would do it, other times not. I made sure the LM terminals made good contact and cleaned the TB. Still did it. As 4speed said, replaced the speed sensor and it stopped. Hopefully it won't come back, but if so, try the speed sensor.

[jeff1234]

It is only adjustable in the respect that you can leave the mounting screws loose and tip it forward a very tiny bit. I had three tps's to try. My theory is that when you move the TPS by tipping it towards the front of the car you change the output voltage. This can be seen on the OTC 4000 read out. I initially chose the TPS that gave me the greatest initial voltage reading and then did the adjustment to get more output. This stuff is a complete guess, but it worked when nothing else, such as resetting the idle, cam timing etc. fuel pressure had any affect. So......