Car jerks when releasing throttle *only when hot*

[sohcmyevo]

Hiya, greetings from New Zealand! :d

I have a 2003 Mitsubishi Galant with GLS trim -- has a 4G63 SOHC motor paired with a 5 speed transmission (as far as I can tell, the car was imported specifically for NZ, Singapore, and Hong Kong markets.) I know this is a VR4 forum but hey, gotta give the poor spec models some love too right? I've been having a problem related to the throttle, specifically at low speeds. The car likes to jerk quite aggressively when releasing the accelerator especially in first gear and the only reason why I know this is a problem (and not just because of mitsi style), is because it doesn't do it when it's cold. No matter how gently you release the accelerator the car will jerk once you reach a point of around 2 mm of travel on the pedal. On off On off On off is the only way I could describe it, as if there's like a deadspot on the accelerator pedal. It's especially irritating in stop and start traffic, but otherwise it's not really a problem although it still can be felt in all gears. I also get really poor fuel ecnomony, totally off from what it should be (not sure if it's related however). Except from all of that, the car runs perfectly fine.

I have tried to diagnose it to the best of my ability. I tried changing the fuel filter in combination with fuel filter cleaners, replaced the air filter, and I've checked if there are any engine codes using the paperclip method on the MUT-II/OBDII port which there are none. I've pulled the MAF sensor to see if it's affecting anything which it isn't. I'm just not really sure and would really appreciate the help or advice if anyone could offer any. I've checked the linkage on the throttle which is fine, including the throttle plate which looks completely normal with no play in the mechanism. I was thinking there may be something wrong with the TPS but the car seems to happily rev in neutral and otherwise works fine when cold, which makes me think there's something that's changing (or not changing when it's supposed to) when the car runs hot -- I don't think a component disconnected from temperature or that is non-pneumatic would affect anything.

Cheers guys I'm open to literally any advice rn lol. /haz (Oops just realised there's a section for non-vr4s, move post at your will haha)

[foxdie]

Hi Anthony,

Yep this is screaming TPS failure, as it heats up I'm guessing a weak electrical connection is breaking circuit. Make that your next check :)

I'm unsure with the GLS but the V6's have a separate "throttle closed" switch too built into the same mechanism, if that's not marking the throttle as closed that could also be causing an issue.

[sohcmyevo]

Hey Jason,

Thanks for the reply. Your advice makes me think you're probably right especially considering I now remember I've had problems with the TPS in the past specifically causing the car to stall at very inconvenient times. Jump-starting a car whilst travelling at 80 km/hr was something I found to be pretty scary haha :2thumbsup. I'll investigate the sensor in the weekend and make sure to follow up.

Cheers mate.

[sohcmyevo]

Hey-ya,

I managed to pull the TPS off the galant today and funnily enough, the car behaves as if nothing had even been chanaged under the hood. From what I can tell, the jerking seems to have disappeared which is great :happy: Investigating further with a multimeter, testing pins 1-2 of the TPS gives a gradual and consistent change in resistance which seems normal. However, as you were saying earlier with the problem may being something to do with a throttle switch, if I test pins 3-4 for continuity which are the diagnosis points for the throttle switch, something interesting happens. When fully closed there is continuity between pin 3 and 4 and when fully open there is none -- just as a fully working tps should behave. However the continuity seems to drop suddenly to zero in the first 20% of the acutuator range, rather than gradually changing throughout one rotation. This would make sense for this to serve as an explanation for my issue, but I'm wanting to confirm if this seems ab-normal. I'll be driving the car without the sensor for the next few days to confirm if the TPS really is the issue, so I'll keep you posted.

Edit: Come to think of it, this could even explain my bad fuel ecnonomy as once I push the throttle past 20%, the car thinks that the throttle is fully open which it isn't. Hmmm maybe what do you guys think?

Cheers.

[sohcmyevo]

81143

[Amonlym]

I would have through that the switch on 3 and 4 should change at below 5% or something, otherwise it sounds fine.
With the TPS off I would assume you will have worse throttle response, but as the car doesn't use an e-throttle it probably runs fine as it will default to tables or just use the closed loop fueling to work itself out.

perhaps its a wiring issue on the TPS signals?

[sohcmyevo]

Hello,

I did forget to post back on what I found so here it is. I decided to take a risk and buy a 2nd hand tps. I went to the scrappers and pulled a tps off an old crashed legnum. Car works flawlessly now -- zero issues with the throttle. Foxdie's guess was spot on. I think it was most likely to do with the throttle closed switch not working as it should have been the switch was activating way too late. Didn't bother testing the 'new' tps but you'd probably find that it activates below 5% as Amonlym has said. Thanks so much for your help guys (both of you) I appreciate it /thankyou

[BBVR4]

hi my car jerks in from stop to taking off thru gear changes and when in in 5th at 2500-3000rpm but give it some gas and it stops also using to much petrol just installed my wideband sensor in yesterday and it sits at 22.4 at idle went round the block and it all over the show what is the afr at idle for our cars


any help appreciated

[galantnight]

At a guess I say you have a big air leak and AFR at idle should be around 14.6 have a look a see

[BBVR4]

ok thanks i will