Just noticed this in the last week: Standing starts are generally fine. However, accelerating from slower speeds at low rpms initially feels like no response from throttle. I connected to scan tool today with these results.

Normal oper temp - 195 - 203F. Intake temp 91- 105F. Fuel press avg 55psi. MAF idle at 56cfm with max seen under accel of 560cfm. Vacuum at idle is 15, high of 24 under decel and low of 1 under accel.

I noticed 2 things that I don't know if they are normal. The timing runs around 24-36 advance at cruise, 10 under deceleration. When I accelerate in third gear at around 2000 rpm, the timing goes to zero to 5 degrees advanced. Downshifts occur properly but gently pressing more throttle does not enhance acceleration. I also noticed that system goes to open loop under deceleration from highway speeds.

I have no codes or pending codes. All this is with the a/c on or off. Everything works fine, mpg is 22 city and highway (normal), idles smooth as glass. I cleaned the MAF this morning and it seemed like it lessened the lack of power. It has 156,000 miles on the clock. I've done plugs and IMT and intake gaskets about 6000 miles ago, air filter is clean but not new.

I only use premium Shell gasoline which here is 93 octane.

So....in summary, is it normal for the ECM to take away timing when accelerating from low rpm given the high ambient temps and load of the a/c? And is it normal for ECM to go to open loop under deceleration from high speeds? Could the MAF be tired?

 

This morning it was 71 and rainy. Normal power after start up and continuing for several miles. Refilled the tank and added Techron fuel system cleaner. Will be replacing air filter when I get home today. Watching the scan, everything appears routine except the drastic cut in ignition timing under low rpm load. Oh for the days of real distributors where one could adjust vacuum, spring and weight rates to suit. And not have a computer take over........

 

Found it. Plastic vacuum line from drivers rear of intake to fuel regulator had broken. I was so busy watching other info I didn't watch fuel pressure under accel. Patched it for now will order new part. Guess I should go back to old mechanical checks first then plan the ECM!

 

Glad you got her fixed. I am looking for a new scan tool. What are you using?

 

ELM 327 you can find on the net and ebay. Works with torque app for android. I opted for the upgraded $5 app which has more features. The Elm plugs into the obd port and transmits bluetooth to your phone app. Elm runs about $10.