02 Mitsubishi Diamante rough idle

Jan 13, 2020 9:11AM PST

Hey Everyone,

i have a 2002 Mitsubishi Diamante with about 170K miles on it. My problem is when it is in park it idle around the 2 mark on the dash which seem to be high, but when you put it in drive or reverse it idles very unstable jumping from the 1 mark to almost 0 and feeling like it is about to die but never do. when driving it down the road it surges hard at stop lights like it is trying to pull off then feels like it is about to die. my biggest issue is that it DOES NOT HAVE A CHECK ENGINE LIGHT ON so i don't know where to actually look. can someone please help!

I have replaced:
PCV Valve
IAC Valve
Fuel Filter
MAF sensor
EGR Valve

Plan to replace:
Fuel pump once i burn done some gas out of the gas tank

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Poor idle
Jan 15, 2020 9:20AM PST

Hi, JMorgan; Does not sound like a fuel pump issue. Sounds more like a vacuum leak. Possibly, EGR valve not closing? It's quite easy to check for vacuum leaks with a smoke test, but generally, only repair facilities have them.
Good luck.

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There's a clue in the vehicle age.
Jan 15, 2020 9:40AM PST

The rubber or such hoses in the vacuum system get old and crack. It's an 18 YO vehicle so either you get the test noted by landdchamp (big nod to that) or find replacement hoses and one by one replace them.

DO NOT RIP THEM ALL OUT AT ONCE. That cost someone nearly a thousand USD bucks to fix their car. A seasoned DIY car person can replace one at a time. At least most vacuum lines I've seen. In newer cars, well, that changes.

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