Idle Troubleshooting

[gbmidyear66]

Well, the new injectors cured my rough idle - it now is super smooth (need to try the "nickel test", and my "seat of the pants" dyno indicates a measurable performance improvement. One thing that isn't better is my idle speed.

If I am coasting in neutral, Idle will be about 1200, once I come to a stop - it will drop to 900 (as indicated on tach). I have the Haibeck Prom and flowmasters. I believe the 1200 RPM behaviour is "normal" on a 90 - and doesn't particularily annoy me.

I expected my at rest idle to come down with the new injectors, but it hasn't. I mean - 900 is not a huge deal - but clearly something is not 100% right. I have read through a number of posts and believe the culprit could be ... TPS sensor, dirty throttle body, and of course the usual suspect - vacuum leak.

My question is .... (while waiting for my LT5 Service supplement to arrive) - what troubleshooting steps/sequence should I take to isolate the cause (ideally simplest test to hardest?)

Thanks