I've had the truck for almost a month now and it has been fine but it started sounding like it was misfiring so I changed the spark plugs the old ones never looked like they have been changed so that so so fixed the problem and so I changed the spark plug wires and it ran fine. But now all of a sudden it's idling weird the rpms are like going up then down but not much and it mainly only happens when I have my foot on the brake but when I take it off it idles a little high. Yesterday I was going down the road and I thought the ac button was pushed in so I pushed it to release it but it wasn't on and that's when the problem began but also one of my friends thought it was out of time to he tried to fix it. I'm just confused about it and have no idea if it has something to do with the ac or if its just out of time pls help if you can.

 

If it's happening when you hit the brakes I'd say you have a vacuum leak in the brake booster. The high idle could just be that. You'll probably have to adjust the idle once you get the vacuum leak fixed.

 

Yeah that's kinda what I was thinking. But do you have any idea what vacuum line would be causing that like maybe the one coming from the brake booster? And do you think maybe when the ac kicked on it pulled one of the vacuum lines?

 

if the high idle continues, after you reconnect the vacuum-line going to the booster...you may need to replace the booster.

hth,
manny

 

From what i've understood the reason for the idle to go up and down while on the brakes is to try and bring the idle lower. This occurs when the idle is above 1500 RPMS.

 

You need to check/adjust the idle and timing when you change ignition parts. You don't say what engine or transmission.. 22re 750 for MT 850 for AT, 3vze 800.

What is likely going on is you're idleing to high and the fuel cut off is triggering. If your idle and timing are in spec the next step is to check the brake booster. FSM Link page BR-7, "OPERATIONAL TEST OF BRAKE BOOSTER" step# 2.

 

Oh ok I didn't know that. And is a 22 re

 

I got it it was just way out of time. When I turned the distributor and set the idle lower I took it for a spin and it runs fine now. Thanks for the help

 

It's probably the booster itself, not the vacuum line. Disconnect the line and plug it. Hit the brakes with the engine running. If the problem goes away you know it's the booster. If the problem is still there when the line is disconnected start checking for leaks along that hose. You'll either need to replace the booster or the vacuum line. You'll have to adjust your idle again too.

 

here is a refresher on the brake booster check No need to even pop the hood!