Timing on a 1988 Ford F150 5.0
 

I have an F150 1988 that I bought last year I haven’t done anything to it since I have had it. It has always run rough at idle but when driving it run good. It started running real bad all the time and when you came to a stop it would idle way down, miss bad, and the check engine light would come on I would have to keep one foot on the brake and idle it up to keep it running, also it would run smooth when cold at high idle but when it warmed up it would run real bad. Anyway today I decided to give it a tune up and see if that helps when I got my book out and checked the ignition wire timing I saw that the timing order for the 1988 302- 5.0 is 1-5-4-2-6-3-7-8 when I went to take the wires off the distributor cap I saw that the timing was 1-3-7-2-6-5-4-8 which my book shows to be a 1994 and later 5.0. My question is if this engine is a 1988, I don’t think it was ever replaced, but was timed as a 1994 or later would it run? I would think it would through the engine out of balance or may not run at all. I didn’t finish the tune up yet and am kind of stumped on how I should do the wires. Never ran into this before. Any help would be greatly appreciated.
Thanks

The 1-3-7-2-6-5-4-8 firing order is for a 1988 5.8 litre or a 351 CI engine

The 5.8L or the 5.0 with a cam (think mustang) was 1-3; all other v-8's were 1-5. Take a little care to set the timing to 10 degrees BTDC, and route #3 wire between 4 and 2 and #6 wire between 7 and 8 in the dist. cap to cancel any unintended RFI.