depends on the year.1996 to 1990,some times its low coolant.the coolant grounds the iac,but they do go bad.
Vaccuum valves bad
The Honda Shadow 1100 has hydraulic valve lash adjusters and for this reason no valve adjustment is required. None is mentioned in the manual. But if the valves have gone bad, they can be replaced. This is a job for a skilled and experienced motorcycle mechanic.
Bad compression is usually worn out piston rings, no compression is usually bad valves - assuming it's a 4-stroke.
if it smokes when you first start it, or sometimes if it has a tic tic in the top end intill it warms up
A flashing D4 light on Honda Accords is commonly the result of a bad speed sensor. The speed sensor is located on the transmission and sends a signal to the speedometer and a signal telling the transmission when to shift.
Bad Valves or fuel pump usually from redlining the care
it resets automatically when there is not a problem. if it is still on, there is a problem. you may try bleeding the system and refilling it, otherwise your modulator is probably bad. this is a very common problem in older accords.
The valves can be adjusted on your 2.3 liter Ford engine. Valves that are noisy may be caused by a bad rocker arm.
Possibly and you may also have a cracked head, or busted piston. The only way to know for sure is to remove the head and see what you have. You will have damage but it may not be bad or it may be very bad.
honda's are more reliable Not true! each manufacturer has its good and bad, hondas for instance were known for having bad valves for a while (corrected now Im sure) nowadays they are all good bikes, I either own or have owned them all (brands) and really if you take care of them they are all great, just stay away from china bikes!
I assume by the question that you have a bad ECU, and want to replace it with a used one from the junkyard. I, myself, managed to take an ECU out of a 1995 Honda Prelude S and it runs without a problem in my 1991 Accord. The 1990 to 1993 Accords share the same motor as the 1995 Honda Prelude S, so the computers are interchangeable. Also, you might want to check what engine you have. If you have the F22A6, then the computers are NOT interchangeable.
No but an engine running like that can damage the valves.