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'94 Roadmaster ltd. LT1: Major hesitation, erratic idle and erratic down the road as well, please help!

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
Hello so this is pretty much my last resort before we possibly junk our Buick. The sypmtoms it is having is erratic idle, and major hesitation at any speed, but it doesn't seem to be misfiring from what I know. It just seems like the engine literally seems to wanna die every 5 seconds.
So my dad and I took it to a automotive electrical mechanic basically on accident because we were test driving it a few miles because my dad said the problem it has magically fixed itself. So yeah we test drove it and the problem started happening again right near a shopping plaza, I got scared that it would stop on us in the middle of the road so I pulled into the plaza and it died in the entrance and we pushed it to a parking spot. We suprisingly had a ratchet set in the trunk so we got to trying to diagnose if maybe the air filter is clogged, if there is possibly gas or oil in the throttle body, checking to see if all of the spark plug wires are on, checking all vacuum hoses, and everything basically seemed in tact... there was no liquids in the tb, the air filter was perfectly clean, and there seemed to be no vacuum hoses cracked or loose. We then tried to turn it back on and after about 10 sec it turned back on! We then drove it a less then a quarter mile to a electrical mechanic we know, his shop is literally just across the street from the shopping plaza. So we left it there when he was closed, came back the next morning and told him everything wrong and gave him the keys and after about 8 hours of him diagnosing it he could not find the ultimate cause of the problem. He said in spanish "it is most likely something majorly wrong with the engine" so we then limped it to a friend's driveway and that is where it is sitting right now. What can yall possibly assume be wrong with it? We have changed the following: Spark plugs (NGK iridiums), spark plug wires (AC Delco), both cooling sensors, and supposedly the previous owner changed the optispark a few years ago. If anyone can give me an idea of what could possibly be wrong with it it would be greatly appreciated. Thank you!!!!!
 

Gbuster

Buick Newbie
Sustaining Member
25
2
3
NC
Buick Ownership
Buick
My '94 RM base did many of the same things when I first got it. It was an easy fix: check tightness of the nut which holds the fat cable going into the under hood fuse box. The fuse box I am referring to, is in the engine compartment, on the passenger side, just in front of the firewall, in the corner.

When this nut loosens up, heat develops at the connection, sufficient to melt plastic at the edge of the fuse box. Part of this connection
was made of pot metal, which held the stud captive. I removed the pot metal part, which leaves the main power connection tab sticking out of the fuse box. I used a 5/16 brass nut and bolt, brass flat washer, and a toothed stainless lock washer to reattach the fat cable.

After this repair, LT-1 has been completely normal. The PO was an elderly man who bought it new, and when I bought it from him he gave me the window sticker! I believe it may have left he and his wife stranded on the side of the road when the engine quit (just like it did to me). Hope this helps.
 

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
My '94 RM base did many of the same things when I first got it. It was an easy fix: check tightness of the nut which holds the fat cable going into the under hood fuse box. The fuse box I am referring to, is in the engine compartment, on the passenger side, just in front of the firewall, in the corner.

When this nut loosens up, heat develops at the connection, sufficient to melt plastic at the edge of the fuse box. Part of this connection
was made of pot metal, which held the stud captive. I removed the pot metal part, which leaves the main power connection tab sticking out of the fuse box. I used a 5/16 brass nut and bolt, brass flat washer, and a toothed stainless lock washer to reattach the fat cable.

After this repair, LT-1 has been completely normal. The PO was an elderly man who bought it new, and when I bought it from him he gave me the window sticker! I believe it may have left he and his wife stranded on the side of the road when the engine quit (just like it did to me). Hope this helps.
Thanks for the reply I will definitely get to looking into that fuse box nut later today, I will update with any news
 

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
My '94 RM base did many of the same things when I first got it. It was an easy fix: check tightness of the nut which holds the fat cable going into the under hood fuse box. The fuse box I am referring to, is in the engine compartment, on the passenger side, just in front of the firewall, in the corner.

When this nut loosens up, heat develops at the connection, sufficient to melt plastic at the edge of the fuse box. Part of this connection
was made of pot metal, which held the stud captive. I removed the pot metal part, which leaves the main power connection tab sticking out of the fuse box. I used a 5/16 brass nut and bolt, brass flat washer, and a toothed stainless lock washer to reattach the fat cable.

After this repair, LT-1 has been completely normal. The PO was an elderly man who bought it new, and when I bought it from him he gave me the window sticker! I believe it may have left he and his wife stranded on the side of the road when the engine quit (just like it did to me). Hope this helps.
Sorry I replied late but it wasn't that :( the bolt is perfectly tight and there seems to be nothing wrong with it. Sadly there is no codes and I bought a OBD1 gm code reader and it isn't working much since it's not throwing a single code. I am hoping it's just the fuel injectors since there is a very noticable smell of gas (not smoke... I've had sh*ttier cars in the passed and I know how smoke smells like lol) so yeah I ordered eight $20 each fuel injectors and I'm gonna replace them and if it's not that then most likely I'm gonna sell it.
______________________________
 

Gbuster

Buick Newbie
Sustaining Member
25
2
3
NC
Buick Ownership
Buick
Did you initially pull codes using the paper clip method, or the HVAC readout method (see attached)?
Is it possible that you are reading no codes because your OBD-1 device is not communicating?

You can read many other engine parameters using the HVAC control head, not just codes.
 

Attachments

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
Sorry for late reply yeah I learned the hardway. You cant really pull codes with the paper clip method or the little $30 scan tool either. I used the HVAC controls and I got codes 15 78 and 82. I dont know how these codes are relevant to what's happening to my car though. I think 15 is a coolant temp sensor code and 78 is similar and 82 is for transmission 1-2 shift solenoid code. Who knows it may be the trans solenoid but it even acts erratic at idle in park. Which wouldnt really mean thats the problem.
 

Dirtybob

Junior Member
101
22
18
Buick Ownership
95 RMS
A bad temp sensor (the one located in the water pump) will cause the car to run poorly.

You can test the fan(s) operation by unplugging the temp sensor connector with the car running. Both fans should come on. The fan relays are located under the hood, pass. side, near the cowl. It's not uncommon for the fan motors to die but I have never seen that trip a trouble code.

The only time I've seen the 1-2 shift solenoid code was when the shop that rebuilt my trans forgot to plug in the large connector (pass side of pan). Didn't have 1st. gear either IIRC.
______________________________
 

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
'94 RM limited LT1: Once again I really need help,
I had this problem on my 94 RMW years ago. The EGR valve was old and crusty and getting stuck open.
Poor idle and poor power.
I may get to cleaning that out thanks for the reply.
 

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
Thanks for the reply, yeah oddly enough I already changed that one with a AC Delco sensor a few months ago. I will definitely get to testing it though. Also I noticed what happened when I was attempting the Paper Clip Method, is the cooling fans turned on!! Pretty sure this is a bad thing since the key was on ON and engine off. I'm seriously at a loss right now though this car is very complicated to work on.
 

torres7

Full Member
139
18
18
Lincoln Nebraska
Buick Ownership
Buick RMW
Long shot and might sound dumb but, did you check the knock sensor? If it goes bad it can cause erratic idle, poor acceleration and fuel mileage, etc. In some cars it retards the timing if it thinks something is wrong, which causes the engine to run poorly.
 

Dirtybob

Junior Member
101
22
18
Buick Ownership
95 RMS
If your coolant sensor is new I would take a look at the connector/pigtail. May be worn out...
I replaced all the pigtails to the ICM/coil/CTS on mine since they were a bit sketchy (i.e. could kill the motor wiggling the ICM connector).
Don't know if you're familiar with shbox - lots of good diagnostic info - testing the temp sensor: 4th Gen LT1 F-body Tech Articles
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roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
Long shot and might sound dumb but, did you check the knock sensor? If it goes bad it can cause erratic idle, poor acceleration and fuel mileage, etc. In some cars it retards the timing if it thinks something is wrong, which causes the engine to run poorly.
No I havent at all but I'll do some research on that and get to checking it and possible replacing it. Thanks for the reply. I just hope its not the head gasket(s), or something else majorly wrong w it like the valves or pistons and I'm just unnecessarily dumping money into it and I'm gonna end up junking it lol
 

roadmasterfan

Member
30
2
8
Buick Ownership
Roadmaster Limited
If your coolant sensor is new I would take a look at the connector/pigtail. May be worn out...
I replaced all the pigtails to the ICM/coil/CTS on mine since they were a bit sketchy (i.e. could kill the motor wiggling the ICM connector).
Don't know if you're familiar with shbox - lots of good diagnostic info - testing the temp sensor: 4th Gen LT1 F-body Tech Articles
No I have not checked or changed the connections but I will get to doing so soon. Thanks for the reply and thanks for suggesting the website
 
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