Rough idle on warm start up (20 minutes), 87 7MGTE

[Bru]

I have read the blogs on this issue in the best I could come up with is to try and disconnect the cold start injector.

The issue is on startup after driving car and fully warming up and shutting down for 20 minutes. It idles rough for 30 seconds until I give it some gas then idle is back to normal. It does feel like one cylinder is missing though on acceleration until it smooths out. If I start the car in under 20 minutes after stopping I don't have this issue or if I wait more than an hour. I have replaced the spark plugs and also the idle air valve, and all three coils. Cold morning starts are normal. There is no smoke for loss of coolant detectable. I rebuild the engine five years and 14,000 miles ago. I retorqued the head bolts to 75 ft/lbs. Only a couple moved slightly. Compression is normal. This warm starting issue began in the past couple months. I suspected it might have something to do with the EGR valve because you can mimic a similar condition at any time by applying vacuum to the servo while idling. I disconnected and plugged the servo vacuum line and it's still did the same thing. I thought it might be a leaking down fuel injector so i took the dust cap off of the pulsation damper. The little screw was still in the up position after 20 minutes warm or cold. The spark plug wires are high-quality Bosch silicone but they are 10 years old. I check the resistance and they are all about 1K Ohm each which is well below the 25K limit. It could be a sticking closed injector or valve stem although I have been using redline fuel additives for some time. I also added some Marvel Mystery oil to the oil and fuel with no change noted. The injectors do have 252,000 miles on them. I have checked and adjusted the throttle position sensor and the ignition timing. There are no stored codes. I put in a oil seal replacement kit in the cam position sensor but I can't remember if this issue started before or after.