Jumpy at idle and low-throttle
 

Hi!


My car has started acting jumpy sometimes when starting up but also when driving/cruising at low speed with little throttle. It moves up and down and the engine/computer seems to be unsure of how to act. Sometimes the rev. goes up and stays on 1500-2000 rpm "idling" after start-up. Accelerating works fine.


This has become more frequent and now I'm wondering if any of you has an idea of what the problem is? Recently the MAF was removed due to changing the thermostat housing, can the MAF or its connector be the cause? Taking in air somewhere?


I'm thinking of re-doing the timing, idle/IAC setting and TPS adjustment. Any other ideas?


Thanks for helping out!


BR,
Per

Re: Jumpy at idle and low-throttle
 

Could very well be a vacuum leak. Since you changed the thermostat housing I'm gonna assume you took off the throttle body to get to the thermostat housing. Id replace the throttle body gasket as well as double check all the vacuum lines running to the throttle body. There's a vac line that connects to the underside of the Throttle body right next to the thermostat housing that is easily forgettable, that vacuum line runs under the plenum and connects to your EGR solenoid and Evap canister. It's also plastic which by now is probably very brittle and easily cracked, I replaced mine with rubber hose just the other day after it cracked.

Also tighten up all the hose clamps connecting the throttle body to the MAF sensor, any air that enters after the MAF is a vacuum leak that can cause problems. good luck

Re: Jumpy at idle and low-throttle
 

Thanks for the tips TylerSteez! I'll have a look at that vacuum line nd of course tighten things up (they should be already but you never know). Will be back later!


BR,
Per

Re: Jumpy at idle and low-throttle
 

One more thing: can a leak on the hoses to/from the Evap canister cause this as well?


Thanks!

Re: Jumpy at idle and low-throttle
 

If it's a vacuum line coming from the evap canister then it certainly can.

I'm not sure if you're against smoking or not but you can easily find vacuum leaks by sealing off the end of the maf sensor and then blowing smoke from a cheap gas station cigar into the vacuum line running from the evap canister to the vacuum port on the throttle body. Just unplug the end that connects to the evap can and puff and blow the smoke in the line, the smoke will come out of any place where a vacuum leak is. I used to use carb cleaner to find them but ever since I heard about this way I'll never go back.

Edit: you should also do this from different points like from the brake booster vacuum hose to find leaks in different parts of the system

Re: Jumpy at idle and low-throttle
 

Hi!


I've now tried to find vacuum leaks by looking over the hoses and also spraying "starter gas" (it should rev up if a leak, right?). Also replaced a few hoses, making sure they're tight. No difference!


Rev still jumps up and down at idle and at low throttle. It even died on me at idle at the parking lot. I've checked and slightly re-calibrated the TPS (now 0.55 V and earlier 0.50 volts), took away the IAC valve and cleaned it (not yet back and tested).


A though struck me: can it be the fuel pressure being too low? I'm thinking of replacing the fuel filter and see. How does low/variable fuel pressure affect the engine's running?


Cheers,
Per


PS. Does the fuel filter have to be specific or will a universal do?

Re: Jumpy at idle and low-throttle
 

It's never a bad idea to change the fuel filter and they're cheap enough anyways, just go to autozone and ask for the one for your specific model. I'd also do a good tune up to rule out the simple stuff like cap, rotor, and plugs. And yes any kind of ether(starting fluid, carb cleaner) will cause the rpms to raise when sprayed over a vacuum leak

Re: Jumpy at idle and low-throttle
 

Thanks! After putting back the clean IAC it's til the same... even took out the O2 sensor and wiped clean but that was hardly needed ( O2 sensor recently tested and should be working).


I shot two vidoes and uploaded. Can you or anyone else make something out of this?


First when warm:

Second when still cold or maybe a little warm:

Yes, I'll check the rotor, spark plug cables and hats (plugs themselves are just changed)! Definately will look into changing the fuel filter. It's strange though, it seems to be running just fine when accelerating or applying a bit more throttle (which generelly means accerelating :)).


Cheers,
Per