Code 33 and bad idle

So every now and then my 91 Roadmaster with the 305 will develop a stumble. Sometimes it goes away and sometimes the car stalls after idling roughly. I get the code 33 when I jumped the terminals. This doesn't happen often but I would like to get it fixed. Also i did notice that the idle beedle fluctuates while driving on the hyw.
Any ideas?

Code 33 indicates a bum or failing MAP sensor. Among other things, the Manifold Absolute Pressure is used to determine engine load and altitude. It is one of the least expensive sensors you can buy. Early design sensors were easily damaged by a backfire.

Are you referring to the idle air control valve fluctuating? The ground at the thermostat housing could be intermittent. It is the ground for the computer, and O2 sensor. The failing ground caused a rich mixture for my car. It caused a rough idle, and it would stall. It eventually clogged the cat. Cleaning the ground fixed the issue. Anything that has to do with the idle should not affect anything when driving on the highway.

My LO5 will sometimes stumble at idle during warm restart. I have not found the culprit, and mine does not throw a code.

You should clear the code, and see if it resets.

Had the battery disconnected and it cleared the code. Since then it only stumbled once without throwing the code. The second time the code came back and the car would not idle after restart. But after a few minutes it started and after a little of hesitation it drove OK. I had to replace the wire connection at the thermostat as it was almost broken off. I did some reading over here and I tried unplugging the Map while the engine was running. Basically no change to the way the motor run. Is that a sign of a bad map? That suckered is $200 for some reason. Also what is the best source for replacing vacuum lines. Mine still has the plastic lines.

Actually I just remembered that I got a map sensor off ebay, the funny thing with the new map connected the car won't even start?

I spend a lot of time in junk yards. Map sensors are there for the picking. Most of them are the same. I try to get them from similar year cars/trucks with the same type of computer system. They are usually 1 bar map sensors. Supercharged cars can have 3 bar sensors. Did you try cleaning the IAC? Also clean the TBI port for the PCV valve, and replace the valve itself. The hose may be crtacked as well, so check it. The PCV system can cause idle issues, as well as some other odd issues.

Vacuum lines can be replaced with any equivalent size line. The plastic lines and fittings are available from your local parts store. You can bend the lines to match by putting them in boiling water and bending them to shape. If you choose a rubber line, they have fittings to duplicate the OEM lines. Make sure you keep all of the check valves. There is a hot water valve on the passenger's side that is operated by vacuum when you request heat, and/or turn it off.

These are all inexpensive things you can do before spending a lot of money.

Great advice thank you. How do you go about cleaning the iac? Also is I unplugged the map sensor the car still ran, but when I plugged in the replacement it would not even start. Is the replacement one bad?

This stuff:

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You will probably need more than just a can of CRC. The baked on crud almost requires a chisel. The PCV port will require some prodding with various tools, if it is clogged.

I can not say whether the new map sensor is good or not. Try another one. Sometimes a known good one will determine if it is a problem. If I get a part from the junk yard, I will plug it in and test by starting the engine. It could be your spark control module (on the relay bracket right side). It is engine specific (LO3-LO3, LO5-LO5). Diagnostics are difficult without having hands on.

Sounds like I'll need to remove the tbi and do some cleaning. I've changed the pvc but I'll inspect the hoses a lot closer. I did see a crack in the hose that goes from the air box to the passenger side valve cover.  The car is definitely running on the rich side. Hopefully cleaning will help some, I was ready to change the injectors.
Thanks for the help guys

Turns out that the pcv hose was completely plugged. Replaced the valve and the hose. Looks like other hoses look OK. I also replaced the iac. Idles better but it will still stumble, especially on hills. Which is bad since I almost instantly loose my brake pedal.
When car runs and I unplugged the map sensor there was no change.
Replacement map sensor caused a no start scenario. I'm really baffled now

Did you also remove the throttle body a clean out the PCV circuit as well? Crud really builds up in there and has to be cleaned out.

Bill

convert2diesel wrote:

Did you also remove the throttle body a clean out the PCV circuit as well?  Crud really builds up in there and has to be cleaned out.

Bill

No i didn't, i do have the rebuild kit and new injectors so I might take it apart this weekend. What's a good soaking solution for a tbi these days?

I have always used two solvents: Varosol (mineral spirits) and believe it or not, a heavy solution of Dawn dish washing liquid and water. Soak it over night and give it a good brushing all over. The PCV circuit will be plugged with hardened carbon residue. You might have to get in there with a dentist pick to get it all out.

Had two throttle bodies plug up on me, with similar symptoms and in both cases it was the PCV circuit in the throttle body. Also in both cases, the idle air motor was gummed up. Usually a good cleaning is all that is needed. There is a re-set procedure if you compress the pintle when cleaning but would check the service manual for it. Can't remember but it was simple.

Good luck

Bill

So I took off the tbi and cleaned it. Replaced with new gaskets  and new injectors. Put it all back together and it ran fine for 10 min. Now it idles like a tractor. Still throwing 33, while it was isling badly I unplugged the map and the idle went up and ran at a higher rpm. When I plugged the connector back it the map it smoothed out. Then I decided to see what would happen if I unplugged the map connection again. This time the car died. I also replaced the vacuum hose from pcv to tbi and from tbi to map.

Then what happened?

Once I unplugged the map sensor the engine stalled

What happened after you replaced the hoses you stated above? You already told us that it stalled when you unplugged the map sensor.

It just ran badly. Did the reset for the iac. Still the idle jumped all over but the car dove if given more pedal pressure. Just got another map will try again.

Ok, so I replaced the map sensor again and the car starTed and ran fine. This morning when I was driving to work it started to shudder again. What I did notice is that it was around the time it reached operating temp. Stopped for coffee and the car would not start unless I had my foot on the gas pedal. Once it got driving it was fine. No check engine light this time.
What else could it be? I thought for a moment that it could be the brake booster since I loose brakes as soon as it starts to stutter. There is also a bad smell when this happens. I had the cat taken out, I originally thought it was plugged.

The brakes are vacuum operated, and if you loose vacuum, you loose brakes.

If you do not get a code, it is something that is not on the code list. Ignition module, ignition wires, spark module, distributor cap, rotor, oil pressure sender switch (in the oil sender), temperature sensor at the thermostat housing, and the vapor recovery canister valve/line.

Does your fuel tank have some pressure release when you remove the gas cap?

I do get dome pressure come out from the gas tank. Not always.
What could be affecting the idle when the car is warmed up?
Just checked and there is no code after this mornings shenanigans

The temp sensor at the thermostat can affect the engine throughout all operation ranges. It should always have some pressure when you open it. Having no pressure could be a cracked line, liquid in the canister, or malfunctioning valve.

Temperature sensor has been replaced. Does the line from the tbi to the canister valve can be replaced with any hose? Would a faulty egr cause this or the air temp sensor?

You could check the EGR, and its soleniod. A lot of sensors could cause the issue, but some will show as codes. I have not seen a bad IAT sensor.

The hose needs to be fuel hose. I would check the evap soleniod, and the wiring under the front of the engine. The wire bundle tends to have the insulation fused, and sometimes the wires can touch.

Thanks for all the ideas and repsponse. The car run fine for a while, and then it started to shudder a little bit. Threw up the same code again as well. Yesterday things got worse, it would bearly idle in gear and it sounded like the engine was tuning on 4 cylinders. Bad fumes as wall. It would go from stalling and shuddering to high idle. Rpms were all over the place but it would drive under acceleration. I figure it's the iac and I did the recommended reset. Start with foot on gas for 5 sec shut off for 10 second and start again
It did the trick, this morning started and ran fine. For about 15 minutes then it's back to running like it's missing again.
I'm so frustrated atm.

What have you NOT done at this point.

Egr valve, purge canister, tps or the ignition module.
Is there a way to check the canister or clean it. I noticed today that there was no pressure in the tank.

RoadKutter wrote:

Thanks for all the ideas and repsponse. The car run fine for a while, and then it started to shudder a little bit. Threw up the same code again as well. Yesterday things got worse, it would bearly idle in gear and it sounded like the engine was tuning on 4 cylinders. Bad fumes as wall. It would go from stalling and shuddering to high idle. Rpms were all over the place but it would drive under acceleration. I figure it's the iac and I did the recommended reset. Start with foot on gas for 5 sec shut off for 10 second and start again
It did the trick, this morning started and ran fine. For about 15 minutes then it's back to running like it's missing again.
I'm so frustrated atm.

Sounds as if you have found the culprit.  The IAC is binding or hanging up.  For the price, change it out.  May be a misprint but Rockauto has one for 10 bucks??? [You must be registered and logged in to see this link.] Even if it is a misprint, even the AC Delco one is under 60 bucks.

Cleaning it works most of the time but if you inadvertently put pressure on the pintle, you may have done some damage.  They are a little fragile.

Bill

Seriously I payed $60 canadian for the one that is acting up right now. I think I'll replace it with the old one and see if I can get a warranty replacement. Would it not throw a code though? Looks like a lot of the lock tabs on most of the connectors are broken off. Is there a way to secure them other than replacement?

Check your lines for the canister. They are getting old and could have a leak.

I believe you can check the EGR valve by pushing on the membrane, or applying vacuum to it when running. You can also disconnect the EGR solenoid. You should be able to borrow a vacuum checker from one of the local parts stores.

The TPS is a potentiometer and can be checked with a VOM. it should read a smooth variation in resistance from the wiper to either end as you rotate it.

Probably not the ignition module.

I do not know how to check the vapor canister.

You can get the connector bodies, and a pin tool. Remove the pins one at a time, and move them to a new connector. I bought one, and the pin tools are somewhat fragle. I bent it, and bought another.

RoadKutter wrote:

Seriously I payed  $60 canadian for the one that is acting up right now. I think I'll replace it with the old one and see if I can get a warranty replacement. Would it not throw a code though? Looks like a lot of the lock tabs on most of the connectors are broken off. Is there a way to secure them other than replacement?

If the IAC is alright from a circuit point of view, then it won't throw a code unless it goes way out of wack. Did not see where you replaced the IAC but trying the old one, after doing the re-set will verify if the new one is bad (it does happen).

If your connector is a standard "Weather Pack" connector, you can buy new ones, and the tools to remove and replace the pins. If the connector is GM specific, I buy tiny zip ties and use them to keep the connectors solid (some times you have to drill a tiny hole in the connector to thread the tie wrap through).

Good luck

Bill

Sorry. Saw that Fred had responded while I was posting. He won.

Bill

No worries, all this help is greatly appreciated. I replaced the iac because I was cleaning out the tbi. It has new jets as well. Will have to drive it home after work and once it cools off I'll switch back to the original iac.

Well I made it home. Changed the hoses going to the evap from the little valve. Ran new hoses to the egr solenoid and th the egr. The little T connector that's splits from tbi to egr solenoid and the air pump had loose hoses and fell apart in my hand so it got replaced as well. Started fine, hopefully it will stay that way when fully warmed up. Parts guy said no availability on evap canister or solenoid. So hopefully it's not that.

You can delete it if you have to. I know my wagon didn't have one when I bought it.

RedandBlack wrote:

You can delete it if you have to. I know my wagon didn't have one when I bought it.

Delete what?

I believe he is referring to the evap canister. Removing it can cause idle issues. It is necessary to cap the line, and port if you remove it.

Changed iac to the old one. Same thing happens. I did notice a lot of blowback coming out from the breather hose.

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It's running super rich and I don't know what else could it be.

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The ground at the thermostat is the ground for the computer and O2 sensor. Mine ran exceedingly rich until I made sure that the ground was good. That included removing the stud, and cleaning the threads of the stud and the hole it threads into. It eventually clogged the cat, and I had to replace it.

You think it's a bad ground?

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That is what fixed mine. It had the symptom of being grossly rich at idle. It would run at higher throttle settings. If that does not work, I have no further ideas to share.

Cleaning the bolt and separating both wires with new connections. Fingers crossed

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Nope, still running filthy rich. Put in the new iac, did the reset and nothing. Took of the gad cap and there was no pressure escape. Might change the main line that goes from tbi to the evap canister. Other than that bad oxygen sensor? Bad computer? Egr?

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EGR would cause lean mixture. The O2 sensor can be tested. Computer is almost never the problem. If I were throwing parts at it, I would go to the O2 sensor. You can get it out from the top at the left side fender. I have used a crescent wrench and been successful. The connector is attached (supposed to be) to a tab attached the oil pan. You need a small screw driver to get it apart. If you are going to get a new one, get one with the connector for the car. The wire is stainless, and you can not solder it.

New oxygen sensor is only $30, I'll be changing this weekend.

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I ran a jumper cable to the negative just to make sure it was not a ground issue. It's idling rough even when cold now. It's been really pouring the past few days so I have not had a chance to replace the oxygen sensor. But I was wondering if it could be the tps? After I removed it for the tbi rebuild was there a specific adjustment I needed to do?

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So I basically followed this video for the tbi rebuild. Except for the last part where he does the iac reset. I skipped this part because the shop manual says to do it differently. Should I try reset it the way the guy in the video does? It is at the 11:30 mark of the video.

The TPS has a minimal adjustment. You can measure the resistance when it is in place, and the throttle blades are closed. You can not adjust the idle, because the screw is sealed.