I have a 1996 Mustang GT with 129,000 miles. I bought the car to teach myself how to work on cars and preserve a wonderful Mustang. When I bought it it missed under load, changed spark plugs, plug wires, and coils and fixed that. But the car also has a slight surge at 1500 rpms (+100 rpms or so). To address this I have so far changed IAC and PCV valve and hose. What else could it be? Thank you in advance for any input.

 

The next thing I'd do is clean the MAF and throttle body.

Also, I've heard that aftermarket "cold" air intakes can sometimes produce a similar problem...