I’ve noticed a new quirk with my 90 ls. When I’m sitting at a light, with the brake pedal pushed, the idle dips and I get some nasty vibration. When I let off the brake (still just sitting) the idle comes up about 200rpm and the vibration is less (but still there). Anyone have a similar experience?
Also, I’ve noticed my MPG drop from 31 to 27. Maybe its just the winter gas, but I’m wondering if the two simptoms are connected some how. Also I ran some seafoam through the intake last oil change hoping that might help the rough idle, but it didn’t do much. In fact, I’m wonding if it made things worse!
With 155k I’m not expecting much performance from the engine but I need my Teg to last another year! Fuel filter, air filter, plugs, wires, cap and rotor are only 3k old. Should I look at the O2 sensor? New injectors?
check your ground cables maybe. lighting the brake lights should cause a slight dip in engine speed, then the computer should adjust the airflow to compensate, and it should come back up.
Also could be a vacuum leak in the brake booster, though I would expect idle to jump up then. You could try removing the line from the brake booster, plug it temporarily, and see what happens when you hit the brakes.
I have the reverse problem. My teg idles about 200rpm too low and when I push the brake pedal hard, the revs come up. I also have just replaced the ignition coil, distributer cap and the ignitor (ignition module) but that was because when driving, the car decided it was tired of running and would just stall out and die, then after a few minutes would fire back up and go for a bit, then die again. Any guesses on that??
The idle drop is from the vacuum booster on the brakes not able to maintain a good vacuum due to your master cylinder seals being gone, and air getting past them.
This has happened on every Honda I have owned. Replace your brake master cylinder and vacuum booster. Most likely you will also find your brake pedal won’t slam to the floor anymore before the brakes have to engage.
I have the same exact problem and my brakes feel solid as well but I was told by a Honda Mechanic (been with Honda for 30 years) that my booster is bad; so that explanation of the cause of the shaking makes perfect sense, but it could be something else as well but everything else checks out ok.
if you change the brake booster u do not have to flush the system, lol, it actually has nothing to do with the fluid besides pushing the master pistons in. then the master takes care of the fluid. if you hit the brakes like someone stated and the rpms drop your booster is bad, small vaccumm leak in the booster. if you want to check connect a vacumm gauge to the booster hit the brakes look for drop in vacumm, if u leave it alone eventually u will get a very stiff pedal… change the booster