Hello, thanks to all here for the info I've already found about my issue.
I've been able to test a bunch of things but this problem eludes me.
The car starts, idles, and runs fine, except that when you let off the gas for more than about five seconds, when you step on it again it hesitates and stumbles majorly.
This was getting worse previously to the point where it would stumble all the time and had little power. I had the sending unit and two fuel pumps replaced at that point as well as timing, timing belt, dist cap and rotor, spark wires. then it worked with the stumble only present on acceleration as described.
I've tested the o2 sensor and it seems to be working well, showing 1v and varying up to there with accelleration etc. Cleaned the AMM and the intake hose between it and throttle body. Checked for vacume leaks with propane and soapy water to some extent.
tested fuel pressure regulator by taking off vacume to it. this does not change engine idle as described! do I need a new fuel pressure reg? is this the problem?
Tested AMM as per FAQ and other posts. my meter is dodgy but it looks like it is working: tested between pins 1&3: 1.4v sitting, 2.5v on idle, 3.3v on rev.
BUT!! whacking the intake hose next to AMM makes car stumble simmilarly to how it does when problem is present in driving. whacking anywhere else doesn't replicate the problem. further, AMM voltage test does not vary when whacking makes stumble.
Codes that usually come up during driving are 2-3-1, 2-3-2, 1-1-3 showing lambda and o2 compensation problems I think.
So, any ideas? Is it AMM, regulator, mystery vacume leak?
I'm out of mechanic money at this point....