99' GM noisey valves

[bmkj02]

I have a 99' Mercury Grand Marquis. I read everywhere that it is made to run on 87 octane. Whenever I use 87 octane the valves rattles A LOT on idle or wide open throttle.When I use 91 or 93 octane it runs fine. From what I read it shouldnt do that at 87 octane. Any ideas on why. Is there something wrong with the valve train??? With the price of gas I rather keep it at 87 but dont want to damage anything. Cant adjust the timing since this is a distributorless car. I would have to purchase a timing adjuster if I wanted to do this. Please help.

Thanks
Bill

[way2old]

Have the vehicle checked with a scan tool that can read the parameters. Look at the BARO for the MAF sensor. Should be somewhere around 155. If it is way lower or higher than that, either clean or replace the MAF sensor.

[danielsatur]

How many miles are on the car?
Are you on schedule for routine maintenace?
When was the last time plugs were change?
Does this year have Sparkplug coils?


I had a TC one time with same problem and the root cause was sparkplug
wires.

MCGIVER

[bmkj02]

It has 71k miles on it. No spark plug wires. It was the 8 coils. I changed the plugs about 5-6 months ago. It has a newer air filter about 5-6 months old and a fuel filter changed around 3 months ago. Oil change every 3-3500 miles.

[rhandwor]

I think the knock sensor should retard the timing to control this condition but this requires a new sensor. Take a small hammer and tap beside the sensor and see what happens.