P0300 and P0400 Causes

[Rock2610d]

My computer stored these two codes at the same time.

P0300 Multiple Misfire
P0400 Exhaust Gas Recirculation Flow Malfunction


Car felt like it was missing badly under acceleration. Looked at A/F Ratio and it was at 17 or so....pretty lean. Let up a little on accelerator and than pushed down again and started missing again....A/F ratio still at 17 or so.

So, I let all the way up on accelerator and pulled a hard vacuum and misfire went away and A/F ratio is normal....14.5-14.7.

Car has all new oem sensors, Plugs only have a couple thousand miles on them and wires 8mm, EGR Valve is very old though. I have had to let off accelerator every time I boost over 10 psi to pull hard vacuum so my A/F ratio will go back to 14 .7 or so from 12.8 or so. This is the first time it went lean and missed though.

I do notice that there is a solenoid or something under the hood that vibrates once in a while....when it does my A/F ratio goes from 14.7 to 12.8 or so. Not sure its related to the above issue but want to give you that detail in case its important.

I have not boosted over 10 psi since the above happened and car runs perfect....put over 30 miles on it and no more misfires or anything.

Any Suggestions?

 

[Sitro4g63]

Try cleaning out the ports and valves of the EGR. They may be clogged with carbon deposits. Try shooting carburetor cleaner in the intake manifold. If so, that is why your getting the Exhaust Gas Recirculation(EGR) flow malfunction. Which could also be the problem for the missfiring. Clogged EGR valves dont allow the right flow of air to get into the intake manifold, therefore making your computer think the intake manifold is not recieving enough air, which gives you a high Air-Fuel(A/F) ratio. And while pulling a hard vaccum, it sucked the excess air in the combustion chamber, therefore giving you the proper A/F ratio. All together my advice is to check those valves, clean them if you can or just replace it.

Also does that solenoid vibrate separate from the engine or with it? It also maybe the vaccuum control soleniod to the EGR valve.

 

[koafallenangel]

the misfire could be cause by a faulty coil pack, spark plug wires in the wrong firing order or simply just need to change the spark plugs. Hope this helps! I just delt with this myself.

arareare also if the plugs are new but gapped too big it will cause misfire.

 

[Rock2610d]

Yah, I am leaning toward the EGR valve or its solinoid too. Just a little confused on how it could cause a lean condition.

So, I suppose a 17:1 afr would be lean enough to cause misfires?

UPDATE***********************

Well I found a couple of issues.
1) #4 spark plug was gapped at .040, I installed them and cannot imagine missing this. Other 3 were right on .028 inches. Re-gapped #4 to .028.

2) EGR's bottom bolt was hand tight when I removed it. I cleaned the EGR with carb cleaner and reinstalled.

Car boosts to 15 psi with no issues. Motor sounds a little different now....more throaty I guess. Plus I cannot hear turbocharger as well as I did before. Its more muffled.

Was getting 27 mpg prior to this maintenance and hope to get better now.

One last thing....before this maintenance my Air Conditioner would pull motor down to under 500 rpm at idle. Now it does not, my OBD scanner showed around 900 rpm at idle with the ac on. I must have had a minor vacuum/boost leak at the EGR valve.

I would like to show this thread as resolved but do not know how! SORRY

 

[Rock2610d]

Well, I thought it was fixed! 150 miles later both codes reappear, and car sounds like a VW bug.

Car bogged down, A/f went way lean. Not boosting just cruising at 65 mph. Took it out of gear and let it idle while coasting and reinguaged, misfiring quit but car still sounds like a VW. Sound of VW has been there since I cleaned EGR.

Any ideas?

 

[Rock2610d]

Well, I found 2 more things wrong. Cracked Emissions valve nipple and bad EGR valve.

1) The 1 way valve on the hose from emissions canister to fuel tank had a cracked nipple. Replaced it with a new OEM unit.

2) The EGR valve that I thought was good was in fact not. Installed a new OEM one.

3) Installed a new OEM emissions valve that has multiple vacuum lines on it. One hose goes to turbo intake between turbo and air filter.

4) installed new OEM solenoids on firewall, I think one is for fuel pressure and one is for Evap canister.

Rode it hard and then whipped it rode hard some more....pushing 15 psi boost and 5000 rpm. VW bug sound is gone and no codes yet.

I will drive it next week and see if I have fixed the issues.....I HOPE I DID.

$200 worth of new OEM parts.