Do you dare venture into this Riddle, masked as an Enigma wrapped in a Conundrum?
 

Hello folks,

I've been a Saturn user for some time now, and I've grown quite intimate with the Saturn SOHC engine.

Not too long ago, I purchased a '93 Saturn with nearly 190k miles on the original ticker. The previous owner didn't know too much about the mechanical history of the car. So, I decided to pull the engine and Tranny and rebuild them both. I did this, and the car ran quite well for about a year.
At 193k miles;
Rebuilt the SOHC 4cyl Engine, Vin 9 Engine, replaced all the gaskets, etc. Drilled holes in the pistons to alleviate oil burning issues with these engines, Timing Chain case with hole to oil Timing Chain
Rebuilt the 5-speed Tranny
New Clutch

This winter, as the temperatures became colder in the morning, it became evident that the engine DID NOT want to idle in the cold weather. After the engine warmed up, it would idle better, but it was missing and hesitating during acceleration.....

Here are a list of things that I've recently implemented to fix the COLD AIR idle (as stated earlier, when it's warmer outside and the engine is warm, it will idle just fine), the hesitation and missing.

• Replaced the IACV (Idle Air Control Valve). I've actually done this with several IACVs, just to make sure I didn't have a dead one out of the box. I've pulled 3 from the Salvage yard, and one brand new one with a lifetime warranty from Autozone. The problem has persisted despite these changes.
• Replaced the MAP Sensor, again using several MAP sensors to test this avenue
• Replaced the TPS (Throttle Position Sensor) with a GM brand sensor
• Replaced the ECTS (Engine Coolant Temp Sensor), twice
• Replaced the ECTS Connector
• Replaced the Coolant Temperature Sending Sensor
• Replaced the Coolant Temperature Sending Connector
• Replaced the Air Charge Temp Sensor (located at the bottom of the air intake tube)
• Replaced the Fuel Filter with a Wix Fuel Filter
• Replaced the in-tank Fuel Pump with the Fuel Sending unit
• Tested the Fuel pressure after both of the above were replaced; 29psi at idle
• Replaced the O2 sensor, located in the Exhaust manifold
• Replaced the Cat with a straight pipe (no emissions where I live, will get another cat after figuring out what the problem is)
• Replaced the Flex-pipe and down-tube exhaust, as the old flex-pipe was rotting out
• Replaced the Spark plugs with NGK BKR4E-11 plugs, gapped to .040 (Electrode Core: Nickel)
• Replaced the Spark Wires with MagneCor 8mm wires
• Replaced the Crank Position Sensor
• Replaced the Throttle Body gaskets, ensured the Throttle Body was clean
• Replaced the EGR Valve Solenoid
• Replaced the EGR Valve
• Created a 1/8" steel block-off plate for the EGR valve (currently running with block-off plate)
• Replaced all vacuum lines that run to throttle body
• Replaced the Vacuum Canister Purge Valve
• Replaced Engine Computer
• Tested each electrical connection from each sensor all the way to the Computer, all tested good
• Replaced both Ignition Coils
• Replaced the Ignition Control Module
• Ensured that the #4 Spark wire was NOT touching the #1, 2 or #3 wire
• Last year when the engine was rebuilt, I replace the Fuel Injector (has less than 30k miles on it)

After all of this, this morning when it was around 32*, the car would not idle. When I sat there keeping it alive by blipping the throttle, the temp climbed to normal operating temp. After the engine was nearly at normal operating temp, it would idle...but it was still rough. Driving to work, it was consistently missing and loosing power during acceleration. At one point I was quite concerned that I might end up on the side of the road, kicking my car.

Any thoughts on this Conundrum? :confused:

i guess not
 

Just to add to the conundrum....

The temperature this morning was 30*F, when the car was doing very poorly.

Today, while running an errand, the temperature is 51*F, and it idles fine, and does NOT have any hesitation when accelerating.

I don't see where you ever cleaned the carbon out of the EGR passage on the intake. Have you even checked that to see if it's clear?

Well, it's my understanding that when it starts up, it's running open loop so it is not adjusting stuff based on feedback from anything other than the MAP and ECTS (for air / fuel mix).

It then switches into feedback air/fuel ratio control, and uses the O2 sensor reading as feedback along with the other sensors to correct the air fuel mix to meet emissions requiremens.

Closed loop control is reached when
--O2 sensor output varies
--Coolant Temp is above 68 F
--PCM has received an RPM signal over 400 rpm more than 1 minute
--a change in throttle position is detected.

That being said, at startup it's looking at map and ects.

1) Where did you source your ects from?
======> source brass tipped ECTS and connector from GM dealer
Brass tipped. Not anywhere else (not saying you didn't already, just noting how crucial this is). Please confirm that you have done so.

2) What dies it idle at when it settles down? For a 5 speed SOHC it should be 700-800 rpm. Any higher and I would suspect vacuum leak.

3) What if anything did you do to the head during the rebuild? Might have a intermittent temperature sensitive sticking valve, lifter, etc which, once warmed up, expands and behaves normally.

I VAGUELY remember having a chat with a very knowledgeable Saturn tech who told me that some of the earlier ones had a condition such that the valves would not always fully close on low temp starts. Didn't ask why as my 92 SL2 only exhibited a truly minor case of this

Please let us know the response to 1 to 3 abiove so we can help you out

Rubehayseed - > Not only did I clean the EGR valve, but I replaced it with a new one. Currently, I'm running without an EGR valve, and a 1/8" steel block-off plate that I made. Generally when people are testing the EGR function, they will use a cut up aluminum can as a temporary stop block. I created a steel plate that is a little more robust and can be used in the future, should I need more testing, after this conundrum is eradicated.







I purchased one from Autozone, another from the Salvage yard, and then another from RockAuto.com. In each case, they were all the new style Brass-Tipped sensors. I have not sourced it from GM, however that is worth a try though. Looking over the NalleyGmc Engine templates, i can see the parts aren't too expensive. I may purchased a MAP, ECTS and ATS from GM, just to eliminate that avenue of thought.

http://parts.nalleygmc.com/images/pa...09ZZ00-011.JPG



Correct, it idles at 750 solid..... when it does idle. When the temperature is around 50 degrees + outside, the car does great. But, in the cold mornings, it just doesn't want to go anywhere.




I did have the head professionally cleaned, the valves checked and redone if necessary.
My site, showing the rebuild: https://sites.google.com/site/hunt4steve/saturn/engine



Interesting. This could be the issue. As stated earlier, in warmer weather, the car runs superb. Plenty of power....in fact, I actually tow a HarborFreight trailer with my dirt-bike and camping gear loaded on the trailer. The problem has only surfaced during these cold mornings.....In the afternoon, when the temp goes up, the car runs good.....

Good to hear you had the head done. Was kinda worried when you didn't mention it initially. It's worth a look back at the invoice to see what if anything they did to the valve guides, valves, and which ones. If they replaced valves get the part numbers of what they used and cross ref to GM part numbers to be sure they used the right valves. Also check to see if the head required shaving to true it up.

Did you check the block for trueness?

Try this on a cold morning:
Pull the injector fuse, then do a compression test on an ice cold engine. This should give you a picture of exactly what's going on in the morning on a cold start.
It will also give you the opportunity to check the plugs for oil or gas fouling.

Also do a traditional wet and dry compression test at operating temp.
Please post the results.

Maybe some type of deposit on the valve stems? I don't know, just guessing here. Try running some Seafoam through the engine. Pull the vacuum hose off the power brake booster and with the engine running, slowly pour the Seafoam in through that hose. It'll probably smoke like a diesel, but that will help clean any crap out of it. I didn't realize you could optionally run with or without an EGR on a car that came with one. That's interesting. BUT, you didn't say whether or not you'd cleared the passage of carbon deposits. Air is crucial to these engines.

dang it Rube! that was to be my next suggestion, AFTER the compression tests so we could capture the here and now before we try to clean it.

That's why we all work together on things here.... :)

Sure it was, derf, sure it was. LMAO

Thanks guys for the suggestions. Unfortunately, I leave for work at 6am, so attempting to test things during a work day is pretty much out of the question....besides, it's too darned cold outside. This Saturday, I'll check the compression on the cold engine. I'm also considering making a smoke machine to test the vacuum system....just to ensure that there are no gross leaks in the system. In the meantime, I've ordered a brand new EGR Valve solenoid and a rebuilt Fuel Injector. Eventually I'll get to the bottom of this riddle.