jstluise

'87 SR5, 22RE

I am having an issue of my idle surging when warm. Sometimes it idles normally, but other times it starts hunting slowly (small swings) and gradually surges more and more until the swings are so high that it almost dies (I haven't let it die but I bet it would).

I also notice that when letting off the throttle, the RPMs drop well below idle and then recover to the normal idle speed.

Before I started noticing the idle surges, I did notice my idle speed was a bit lower (150-200 RPM) than normal. Before all this started my normal idle speed was around 800 RPM IIRC.

I was also getting a check engine light briefly (1-2 seconds) right after starting. It was intermittent, and I actually haven't seen it in a while.


I pulled codes 2 and 6, VAF and RPM sensor circuits. Not sure what that gets me. Figured the next thing to do is check my TPS; the last time I checked/adjusted it was 8 or so years ago...

Any other insight?

thebigyank

Check you coolant level. My radiator used to leak, and whenever coolant was low would surge as described

jstluise

Thanks, I'll check the coolant.

I haven't had a chance to mess with it any further, but I did discover something else. I noticed that the major throttle surging only occurs when the brake is applied. Without the brake applied the idle hunts a little bit but eventually settles out and idles fine. When I have the brake applied (sitting in traffic) it will really surge and even died on me once.

From some quick research, this seems to be common when the idle is set too high. Something with the way the computer interprets the brake signal and cuts fuel to the injectors. From what I've read, high means above 1000 RPM...I've never seen my idle above 850.

Since I have never had an issue like this, the first thing I am going to do is verify the TPS is adjust and working correctly. I'll double check my timing and coolant level before moving onto anything else.

gunpilot

2 things helped my idle.


1st- completely remove the idle adjustment screw from the top of the throttle body and put Teflon tape around the threads. Reinsert and adjust.


2nd- clean out the coolant line running from thermostat housing to the idle air control valve under the throttle body. This includes removing the small metal 90 degree pipe on the thermostat housing. Mine was clogged with RTV and rust. I used a small drill bit to run it into the pipe to clear it. This will require you to loosen the top portion of the intake manifold so you can get that pipe out.

Don't forget to top off with coolant as you will loose some.

jennygirl

Sounds like it needs a good burp!

1. Park nose up on the steepest hill you can find or jack the car way up in the front, trying to keep the car level from side to side as well
2. Allow some time for the coolant pressure to subside, then carefully remove radiator cap (I would use a rag or something to shield yourself just in case)
3. Start the car and get your funnel and coolant ready, standing in front of the open radiator
4. Wait for t-stat to open, watch coolant level rise and fall, wait for air bubbles to belch out
5. SLOWLY top off the radiator when the level dips
6. Do this a number of times, until no more air bubbles come out- should take anywhere from 15-30min depending on how much air you have in there

Hope this helps! I did it to mine and it made an absolutely massive difference with idle and startup!

Odin

gunpilot-
One of those holes for the thermostat housing doesn't look so good. Did you have to install a helicoil or an insert?

jstluise

The truck has been running okay for the last few weeks. Something is still up with it, but the surging hasn't been as bad as before...and sometimes it idles and runs normally. Tonight I had some time to pull the throttle body and check out the TPS. The TPS checked out fine, unfortunately...I was hoping that was my problem.

The other thing I noticed with this colder weather is a rough idle at startup (missing). After a few minutes the miss goes away and the truck warms up normally.

I read a bit more about the code 6 and how it is related to ignition (wire, ignitor). That could be where my miss is coming from but not sure that is causing my surging. I am due for new plugs, so I might as well do cap/rotor and wires (I'm not sure when the wires were last replaced if ever).

As far as the code 2 goes, I don't know. It has to do with the AFM, but I have heard about other stuff causing this code to be thrown...that is why I was hoping it was my TPS.

I'll make sure I don't have any air bubbles, and I guess my next check would be with the air control valve to see if it might be plugged. Or maybe it would be a bad connection at the water temp sensor.