PO300 at cold start

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PO300 at cold start

O2 Formula with 75k was throwing a PO300 code on cold start, once it warmed up it ran perfect. No other codes and plugs-wires all check ok.

I found ALL the intake bolts were loose, easy fix!

I can't believe how loose they were, I turned them ALOT to get them tight again, I'LL bet over two turns just to get to 75inlbs. I'm not going any higher even though it calls for 89inlbs. I don't need any broken bolts to fish out.

Last edited by O2Form; Dec 4, 2010 at 09:18 PM.

Dec 6, 2010 | 12:33 PM

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From: Naples, FL

Wow same thing happened to me today, po300 code with cold start. It was the coldest day of the winter here so far, about 18F last night. Started it this morning, SES light was on, actually not just on but BLINKING, ran like crap. Took it to get scanned over lunch at autozone, showed po300 code, they cleared it though, and now it's running fine. Well, I've only driven it about 3 miles since they cleared it, but so far the light has stayed off. And it's running fine too. I'm assuming it's because the car is warmed up now and the outside air temp is a few degrees warmer now that it's noontime. I just hope this doesn't become a regular problem. I'll check my intake bolts since that's the tip you gave. Just to be sure I know what you're talking about, they are the actual bolts holding the intake manifold on?

Dec 6, 2010 | 03:46 PM

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Well I guess I found the intake bolts, the ones that are pointed straight down. I think there were 10 of them. They were a bit loose, I tightened them up..not sure if that was causing the problem, but I read some other threads about the po300 code and someone said that a common thing that causes it (well I guess there are many things) is it could be a cracked vacuum line. They said the one coming out the right side of the throttle body is a common one to crack, I looked at mine and sure enough it was cracked too. I duck taped it as a temporary fix...it the problem doesn't return I'll assume it was either the cracked vacuum hose or the intake bolts as the culprit.

Anyone want to add anything here?

Dec 6, 2010 | 03:51 PM

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Quote:

Originally Posted by staledog

Well I guess I found the intake bolts, the ones that are pointed straight down. I think there were 10 of them. They were a bit loose, I tightened them up..not sure if that was causing the problem, but I read some other threads about the po300 code and someone said that a common thing that causes it (well I guess there are many things) is it could be a cracked vacuum line. They said the one coming out the right side of the throttle body is a common one to crack, I looked at mine and sure enough it was cracked too. I duck taped it as a temporary fix...it the problem doesn't return I'll assume it was either the cracked vacuum hose or the intake bolts as the culprit.

Anyone want to add anything here?

Thats not a vacuum line, its a vent line. Pushes fresh air from the TB to the valve cover when you go WOT.

Most cold start rough running issues are from a dirty MAF.....

.

Dec 6, 2010 | 04:01 PM

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You should use a inch lb torque wrench on those intake bolts. They are very hard to judge how tight they are. I tightened them without the torque wrench then later when I had time I checked them with the torque wrench, I wasn't any where close to what they should have been.

Dec 6, 2010 | 04:02 PM

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From: Naples, FL

Quote:

Originally Posted by LS6427

Thats not a vacuum line, its a vent line. Pushes fresh air from the TB to the valve cover when you go WOT.

Most cold start rough running issues are from a dirty MAF.....

.

thanks, I just figured that out after reading the other threads again..

I just know some people said they had cracks or holes at the bottom of the elbow in that piece and it had been apparently causing some problems.

I guess I'll look up how to clean the MAF if I have any more issues.

thanks

Dec 6, 2010 | 04:04 PM

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From: Naples, FL

Quote:

Originally Posted by O2Form

when you just tightened them without the wrench, and then checked them later, were you too tight from before? or were you even close?

I tried not to get them TOO tight..

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Dec 6, 2010 | 05:23 PM

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Quote:

Originally Posted by staledog

when you just tightened them without the wrench, and then checked them later, were you too tight from before? or were you even close?

I tried not to get them TOO tight..

I wasn't even close WAY too loose yet. The plastic manifold gives alot so as you tighten them the bolts feels tight but its not. Its 10 year old plastic so don't get carried away. Took me about an hr of tigthening until they actually stayed at 75 inch lbs. I'm not going any higher because 10 year old plastic is scary stuff to be moving around. If i were you I would do it with the engine warmed up and take it easy. I tightened them all to 45 INCH LBS 1st which took alot of time because its a feel thing at those low settings. At 75 they feel good and tight, I wouldn't go any higher. I'm going to check them in a month, bet they change alot. Plastic is not like metal.

Remember this is INCH LBS not FOOT LBS, huge difference!

Last edited by O2Form; Dec 6, 2010 at 06:08 PM.

Dec 6, 2010 | 05:51 PM

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Quote:

Originally Posted by staledog

when you just tightened them without the wrench, and then checked them later, were you too tight from before? or were you even close?

I tried not to get them TOO tight..

Someone told me that its the washers that get tight against the plastic as you tighten them down......he said to put motor oil on the washers before dropping the bolts into their holes. Then when you tighten them they won't get stuck, they will tighten all the way to spec the first time.

I have seen builders do this when tightening head bolts too.

.

Dec 6, 2010 | 06:32 PM

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Only time the maf is a issue is if someone uses a oil type air filter otherwise they are fine.

Dec 6, 2010 | 07:21 PM

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Quote:

Originally Posted by O2Form

Only time the maf is a issue is if someone uses a oil type air filter otherwise they are fine.

MAF's get dirty with paper filters too. When you use a filter with oil on it it just gets dirty very fast...............

I've had to clean my MAF at least 5 times in 12 years due to rough idle and missing at WOT. Cleaning the MAF was the cure....

.

Dec 6, 2010 | 07:29 PM

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My 99ta had 130k on it and I purposely pulled the MAF apart to check it and it looked brand new, no dirt on the sensors at all......I can't see what could make it dirty unless oil was getting on it from a oil type filter. The dry air type sheds nothing.

Dec 6, 2010 | 07:38 PM

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Quote:

Originally Posted by O2Form

Its from moisture in the hair (rain, mist, fog, etc) that carries very fine dirt through the filter and onto the sensors. Its just the way it is. You might not get an SES light or rough running engine, not everyone does. But what you have had for alot of those 130K miles is LESS than optimum performance. People who use oil filters are hilarious........and they are marketing suckers.....because the first day it rains, that rain re-activates that oil and it goes right onto the MAF sensors, and from that day on they also have less than opimum performance. Is it a big deal, does it feel like you're pulling a 5,000 pound boat on a trailor...NO...but you have less performance. 130K miles....you've lost alot over time. Its an impossibility to have 130K miles and not have some level of performance loss from dirt build-up on those tiny hair-like sensors, which you would not be able to see with the naked eye......

.

Dec 6, 2010 | 07:41 PM

#15