1987 325es idle surge and delayed throttle response after filling from empty

[robert325es]

Hey, I'm new to the forums so I dont really know if this the place to get help, but I've been having some problems. My 325es is having some issues with idling and throttle. On a cold start, The revs slowly climb up from about 1100rpm to about 2000rpm for about 20 seconds and then drop back down to normal, but then it just surges from about 700-1100rpm consistently. The throttle response is very delayed also when driving. I've checked for vacuum leaks and I have found none. Most of the vacuum lines are brand new, about 3 months old. I've had no issues like this before. I've been driving the car pretty regularly, with no issues, for the past 3 months after I replaced the timing belt and the head gasket. I've replaced the temp sensors on the thermostat housing also. The problem seemed to start after I refilled to full from almost completely empty. I drove it around all day not realizing how low on gas I was (the gas light came on). I filled it up to full, started the car and thats when the surging began. Could some sort of sensor or something be bad? Can it possibly be a fuel pump? Any help would be much appreciated.

It also seems to hold throttle when I give it a small amount of gas when its idling. I would rev it up to about 2k rpm, and it would just sit there for about 10-20 seconds and then it will drop back down and continue surging. The throttle cable is properly adjusted as well. I cant seem to figure out what the problem is.

Thanks guys

[estoguy]

The fueling shouldn't matter. I fill up my Eta every now and again when the fuel light is on.

Check your ICV wiring harness. I had a similar issue, turned out that a wire on the ICV harness had come loose, and it was only working intermittently. Fixed the harness, no problems since.

[dnguyen1963]

How did you check for vacuum leaks? Take out the pump and check the sock. If the gas tank has a lot of rust particulates, running it near empty can clog up the sock leading to weird idle. Tee in a pressure gauge and see what kind of fuel pressure you get when the rpm jumps. A constant pressure will tell you that your fuel pump is probably okay and the problems lie elsewhere.

[robert325es]

Thanks for the responses guys
Update:
So I replaced the fuel filter, injector o rings, and cleaned out the fuel injectors. I checked for vacuum leaks by doing a smoke test. The throttle response is better, but it still surges between 800-1200 rpm now. I haven't tested the fuel pressure yet. That's next on the list to do. I forgot to mention there is a ticking that correlates with increased throttle that wasn't there before. It can be heard in the cabin while driving. I don't know if this is related to my issue, but it seems to be. I've read that it may be related to a fuel pump relay. Does that sound right? I've checked the spark plugs and they seem to be chalky white so I think its running lean.

[dnguyen1963]

Where are you in Indiana?

[robert325es]

I live in Griffith, Indiana. It's near Gary

[dnguyen1963]

Close enough to south bend so if you come this way sometimes we can look at the car together.