Whenever I'm coasting down a hill or simply letting the car glide at a higher speed, the engine will go back to near idle (as it should), but every now and then, the tachometer needle will jump around and you can feel the car slows like you just tapped your brakes and released really quickly. I'll do it a couple of times when I'm going down a hill, but not all the time, what gives? If it's going to be expensive, don't tell me! Just tell me that I need a tire balance or something. Argggggg!

 

I wonder if that's because the engine is missing..
I've had this problem before while cruising around town 45mph.. when I stomp the gas it goes away, bu if I'm just cruising, I'll fell the engine get rough like it's missing a spark or something..

I've been told by a few people that have checked it out and they say they can see the plug wires arcing to different parts of the engine, instead of the energy going to the spark plug.. They said new plug wires solved the problem.

Try that.. usually by this time the OEM plug wires are in need of replacement anyway. it's worth a shot.

it could also be an O2 sensor, but I doubt that.

 

okay okay... i lied... it's not exactly an idle problem. when im' at a light in my 93 SE 5spd, the tach wanders between 600 and 900 (approx). if i ease out the clutch, the rpm's drop to 250, the car moves, but if i push the clutch without using gas, the revs go to 1250 or 1300 and then back down? what is this? normal?

 

sounds normal to me.. that's the ECU in the engine trying to keep it at a normal idle speed.. when you start to let out on the clutch, the engine is under a heavy load and the rpm drop.. so to compensate, the ecu adds more fuel and air and tried to make the engine run faster...

then when you push the clutch back down, the engine is now running freely and doesn't need the extra "boost" it had a second ago. this is what causes the rpm to jump..

as long as it settles back down, that's the important thing.

 

thanks. my 93 toyota didn't have that, and if you didn't gas it when letting the clutch out, it would just die, it never did make an effort to keep the 800 rpm idle if you were using the clutch.

 

My auto does the same thing ... kinda like engine braking. When it reaches 60km/h in 3rd gear, that's when the revs fluctuate, holding the speed at 60km/h as best as it can going downhill.

Perfectly normal.