Toyota Nation Forum banner

1990 celica gt rough, inconsistent idle.

573 16
Howdy folk, in a recent post I was talking about what seemed to be an air/fuel problem so I replaced the air filter and air temp. sensor but when I start it, it runs but the idle bounces between 700 and 400 rpm. I decided to test drive it to see if anything would change but when I would start from a dead stop, it would hesitate/stumble then take right off. When I got back home and put it in park I opened the hood to listen to the idle, it was still rough but idling around 400-700. For some reason I reached over to check the spark plug wires and turned one of the boots and the idle dropped to 200rpms. My next thought is to replace plugs/wires/rotor. I’m open to any ideas of what is going on.
1 - 17 of 17 Posts

· One with the farce
Joined
·
5,115 Posts
If touching a plug wire caused a rough idle, start with checking the plugs and cap/rotor, and check the resistance of the plug wires. Don’t change the wires if the resistance is within spec.
 

· Registered
Joined
·
2,509 Posts
If jiggling the wire causes idle to stumble, the wire is bad. Putting in new sparkplugs doesn't hurt. Just so far, it seems like weak spark to me, because of a bad spark plug wire. You can check spark plug wire resistance with an ohm meter. Generally wires have 10K ohms per foot and more than that can cause problems. Start simple. I hope you don't miss Thanksgiving dinner working on the car and if the simple fix does the trick, I'm happy for you. Also, have the battery and alternator checked. There may be other possibilities, but try the simple stuff first. Good luck.
 

· Registered
Joined
·
13 Posts
Discussion Starter · #5 ·
Thank you Corollacoaster for your ideas and info. on how to measure ohms. It sounds like a good place to start and don’t worry about dinner we are eating soon! This car is an extra vehicle my son picked up and I volunteered my time ( retired ) to do what it takes to get it back to original condition. Enjoy your Thanksgiving Day!
 

· just a nobody
Echo
Joined
·
9,102 Posts
How many miles on the car? If the wires look original and old, just replace them, along with the cap and rotor; something you might consider doing if your plan is to restore the car.
Pull the wire out and inspect the spark plug boot, the spark plug as well. If the idle changed just by moving the boot, it means that it might be arcing to ground.
 

· One with the farce
Joined
·
5,115 Posts
Not always the wires if wiggling makes it stumble. I’ve worked on cars where that’s been the occurrence, but the end of the plug was loose, or the entire plug was loose in the hole.
 

· Registered
Joined
·
179 Posts
Is it worse when it rains? Or here's the old school. A spray bottle with soapy water. Spray the wires and cap, just stalled out? Cap rotor wires plugs. The internal resistance of a wire does not change. But the boots and insulation break down with time. Also what changes is the effective resistance of the spark plug. As plugs wear the gap widens and it takes more voltage to fire the plug. Tired wires/cap/rotor start to leak spark. I have been broke, pulled the plugs, reset the gap to the .005 under and the car ran Ok until the next paycheck.
 

· Supercharzed Toyz Raczing
2 ea Mark 1 mr2's
Joined
·
357 Posts
Howdy folk, in a recent post I was talking about what seemed to be an air/fuel problem so I replaced the air filter and air temp. sensor but when I start it, it runs but the idle bounces between 700 and 400 rpm. I decided to test drive it to see if anything would change but when I would start from a dead stop, it would hesitate/stumble then take right off. When I got back home and put it in park I opened the hood to listen to the idle, it was still rough but idling around 400-700. For some reason I reached over to check the spark plug wires and turned one of the boots and the idle dropped to 200rpms. My next thought is to replace plugs/wires/rotor. I’m open to any ideas of what is going on.
My god man, why the hell aren't you using a $5 multimeter to test ANY electrical parts.Throwing crap at the wall to see if it sticks will put you in the PoorHouse with out a working car. Even worse is taking advice from the internet.

If your nearly antique car has a ISC like my 88 mr2 test it. If not read up on your intake path and associated parts and start testing my good man.
 

· Registered
Joined
·
179 Posts
Not always the wires if wiggling makes it stumble. OUCH! just remember if your heart stops try and grab the wire again before you black out. Wiggle the wire with insulated pliers that is grounded with a jumper wire. Finding a bad wire with one hand while the other is resting on the fender and the jolt goes through your heart.
 

· Registered
Joined
·
4,088 Posts
So did you test your spark plug wire resistance values? If so, what were they?

Also, did you check to see if you had any DTC's (diagnostic trouble codes) that are present or pending? That could tell you a lot on where to look before throwing parts at it.
 

· Registered
Joined
·
13 Posts
Discussion Starter · #16 ·
Hey 93celicaconv I have not checked the wires yet but I did try the jumper wire in the diagnostic port but the engine light did not show any flashing sequence to give any codes, it just stayed solid. As it is now it starts right up and idles at roughly 1200 rpm and when the temp. gauge reaches the half way point the idle drops to 700+/- rpm but continues to run fairly smooth. Not knowing how long ago the plugs/wire/etc. were changed thats why I’m thinking its my next step.
 

· Registered
Joined
·
4,088 Posts
If you didn't get any flashing sequence on your check engine light when trying to perform the DTC code check, you didn't do something right. Normal (no codes) has the check engine light flashing rapidly with no gaps between flashes.

Cold start should have the engine running about 1400-1500 RPM. All warmed up with the coolant temperature in the normal running zone should have the idle speed around 800 RPM. You are close on both, just a little low. I think the 1990 5S-FE that you have has an idle adjustment screw on it that you can adjust to bring the warm idle speed up to 800 RPM - that should also bring your cold start idle speed up just a little as well.

If it runs fairly smooth now, you may no longer have any issues going on.
 
1 - 17 of 17 Posts
Top