rough idle and stalled twice?
 

ive been trying to find a rough idle problem of mine for months now ive changed the plugs to delcos checked tps new cts and this is all ive been willing to bust knuckles on ive been going nuts it only floats on or off 50 rpms when i waiting at a light say and i just learned to live with it but its gotton much bouncier in the past 2 weeks. once it warms up the car is jiggling the fat on me and its friggen annoying. this is my tpi engine by the way. also when going real slow and like pulling into a parking space my car has just very suddenly and quietly stalled out. so now this problem worries me because i dont want to be stranded anywhere. any insight would be helpful thankyou

I'll try to address some of the issues, in no particular order.

First, the factory programming of the ECM includes parameters for a "deadband" tolerance for target idle in both DRIVE and NEUTRAL/PARK. The deadband in DRIVE is often set at 50 RPM, so that kind of variation is somewhat normal. That being stated, the changes are not typically rapid, and thus shouldn't create any noticable shaking, but should be slow and gradual.

Stalling is commonly a result of insufficient idle air. If the throttle body is clean, IAC air passages are clean, and the IAC itself is active, the engine should not stall. There are additional parameters in the programming for minimum IAC counts at a given RPM, and those are generally suitable to prevent stalling.

However, this all depends heavily on the ability of the IAC to respond to ECM signals. If your IAC is only a bit dirty, reaction may be slow enough to allow stalling. Simply spraying cleaner through the TB and IAC air passages is inadequate. The IAC should be removed, disassembled, cleaned, and lightly lubricated. This sill also allow close inspection of the pintle seat and IAC pintle shaft for damage, dirt, and wear.

The vibration at idle may be a different matter entirely, or may be realted. If you have a cylinder(s) that is not making power, it may suffer from weak ignition, improper fuel, lack of compression, or some combination of those problems. Spark plug condition may be a very good indication of the conditions in your cylinders. Another indicator would be a power balance test, which can isolate ant weak cylinder(s). Determine which of your cylinders is not equal to the rest, and you can narrow the scope of your search considerably. After that, isolating the problem in that cylinder will be less of a chore.

Another possibility is spark scatter due to a failing distributor can and/or rotor, but that is more often evident under power, not at idle.