Engine RPM surge
10-29-2014, 05:52 AM
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Engine RPM surge
OK, I posted this on the T4R forum with no luck, so here goes.
A few months back I had a po420 code thrown. Engine ran fine so I didn't do anything about it. The light would eventually go out but then come back on after a week or so. I started having an idle surge during the warm up period ( would idle fine then surge to 2000rpm's for about 20 secs and drop back down ). Didn't do it when warmed up.
I replaced the up stream and down stream O2 sensors and no difference. I replaced the TPS and no difference. I cleaned the MAF and no difference. I must tell you that the up stream O2 sensor was black and sooty. The rear was fine.
Now the surge is all the time warm or cold. Even if you are idling down the road in Drive it surges. At stop lights also you have to have your foot firmly on the brake pedal.
I have also had 2 times when it didn't fire right away when starting and I had to hold the pedal to the floor and crank for about 30 secs until she fired. Any suggestions where to look next?
A few months back I had a po420 code thrown. Engine ran fine so I didn't do anything about it. The light would eventually go out but then come back on after a week or so. I started having an idle surge during the warm up period ( would idle fine then surge to 2000rpm's for about 20 secs and drop back down ). Didn't do it when warmed up.
I replaced the up stream and down stream O2 sensors and no difference. I replaced the TPS and no difference. I cleaned the MAF and no difference. I must tell you that the up stream O2 sensor was black and sooty. The rear was fine.
Now the surge is all the time warm or cold. Even if you are idling down the road in Drive it surges. At stop lights also you have to have your foot firmly on the brake pedal.
I have also had 2 times when it didn't fire right away when starting and I had to hold the pedal to the floor and crank for about 30 secs until she fired. Any suggestions where to look next?
11-02-2014, 07:26 AM
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I would make for sure you don't have any air leaks between the MAF and intake. Check the intake tube for any cracks or loose clamps, especially where the resonator is. Any 'unmetered' air will make your idle funny. If you have access to a scan tool that would help a lot toward narrowing it down, being able to see the MAF voltage and coolant temp on the fly.
Could be a fuel pressure issue, too. A restricted filter (or something else causing low fuel pressure) could cause this.
Could be a fuel pressure issue, too. A restricted filter (or something else causing low fuel pressure) could cause this.
11-02-2014, 07:41 AM
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I ordered a throttle body gasket, actually 2. I'm going to try and clean the IAC. I know I need to check for vacuum leaks also. BTW, what is the black tube, about 1" in diameter that plugs in to the TB intake tube? It is very oily
11-02-2014, 08:00 AM
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That's the crankcase breather. If it's oily you might want to look closely at the PCV valve and the hose that connects it to the TB. Could be crudded up, or the hose could be cracked. That would be a big vacuum leak there.
It's on the passenger side valve cover, at the front.
It's on the passenger side valve cover, at the front.
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