Randomly poor starting and poor fuel consumption

[duffbeer911]

Hope someone may be able to help here. Lately my 4runner has been hard starting about 1 out of 10 starts... it will take quite a few tries to get it started and then it will idle very rough for about 20 seconds or so... either stall or finally settle at about 1000rpm. 9 out of 10 it starts no problems. Once it is warmed up idle will usually go back down to about 600rpm. It is also drinking a lot more fuel than usual .. about 11mpg on my last calculation. I feel like it is also lacking power under stress like up some very steep hills or overtaking on the highway.

I thought it was possibly the IAC so I pulled that off and cleaned it as well as the throttle body but still the problem persists.

Any advice or suggestions most appreciated! Unfortunately I don't have a great mechanic out here (in Sierra Leone) so am working through it mostly myself.

 

[stir_fry_boy]

Fuel filter? I know it sounds counterintuitive, but a plugged fuel filter would cause the the harder starts, but the gas mileage may be independent of the starting issue.

 

[duffbeer911]

ah yes ... it has been a while since I changed the fuel filter and fuel here is really dirty. Are there any other filters in-line aside from the replaceable one?

The mechanic suggested that the fuel pump could be clogged up too...?

He also suggested a transmission oil change to help the milage...? I've never had the transmission oil changed in the 3.5 years I've had it ... so maybe worth doing anyways

thanks a lot

 

[dirteater4]

Transmission isn't going to play heavy on your mileage. Do the fuel filter first and check your tire pressure. Then get into the more expensive stuff ie; plugs, wires, air filter, O2 sensor, etc.

 

[duffbeer911]

Hey again ...

Unfortunately still getting this hard starting problem ... I thought that it was occurring mostly when the tank was full or just after I'd refuelled (or could just be coincidence) ... so put in a new fuel filter and also a new fuel pump. Still getting the problem.

Any other ideas of what to try next?

To recap ... maybe 1 in 10 starts (usually when warm) is hard to start. Sometimes it will start, splutter, stall, and then be really hard to start. Once it is started it will idle rough for maybe 30 seconds then even out and I can drive.

I think it is also running at higher RPM say if I'm cruising along at 25mph the RPM is stilling at about 1500 - 2000. And it is using more fuel than normal.

Thanks for the advice!

 

[jgue467]

Did you say you'd already cleaned the MAF and IAC? :cowboy:

 

[duffbeer911]

I cleaned the IAC and throttle body ... they were really dirty.

Haven't cleaned the MAF because I think I need electrical contact cleaner which I can find here in Sierra Leone. Any thing else I could use to clean it?

Correction - I don't think it has anything to do with how much fuel is in tank! the tank is getting low and its still doing it quite a lot.

I think its getting worse ... or maybe I'm just imagining it... but feels like the vehicle is lacking more power and it is certainly going through more fuel.

thanks for the help!

 

[TheOGConCon]

I cleaned the IAC and throttle body ... they were really dirty.

Haven't cleaned the MAF because I think I need electrical contact cleaner which I can find here in Sierra Leone. Any thing else I could use to clean it?

Correction - I don't think it has anything to do with how much fuel is in tank! the tank is getting low and its still doing it quite a lot.

I think its getting worse ... or maybe I'm just imagining it... but feels like the vehicle is lacking more power and it is certainly going through more fuel.

thanks for the help!

To me (take it with a grain of salt, I'm not an expert) it sounds like your MAF, due to loss of power and MPG. A dirty/broken MAF can result in both of those, because it's not reading the airflow properly, therefore resulting in a not-quite ideal air to fuel ratio.

MAF also could be the reason for the rough start, my GF's 97 Subaru Legacy's MAF went bad, and as a result, it became quite gutless, and would only start approx. 1 out of 5 times, and if it started, would either idle really rough or die.

 

[dsieber]

To me (take it with a grain of salt, I'm not an expert) it sounds like your MAF, due to loss of power and MPG. A dirty/broken MAF can result in both of those, because it's not reading the airflow properly, therefore resulting in a not-quite ideal air to fuel ratio.

MAF also could be the reason for the rough start, my GF's 97 Subaru Legacy's MAF went bad, and as a result, it became quite gutless, and would only start approx. 1 out of 5 times, and if it started, would either idle really rough or die.

FWIW, I'll also second the idea to clean the MAF. I just went through this a few months ago with mine - gas mileage was really horrible, and starting was a bit cranky at times (although it never failed to start). Cleaned the MAF, and things are back to normal. It's a pretty simple/cheap thing to try before spending $$$ on other stuff.

 

[duffbeer911]

ok thanks a lot. Is there anything else I can use to clean it besides electrical contact cleaner? I can't seem to find that anywhere here...

btw, the hard starting/poor milage is definitely getting worse. Now when I have hard starting it is also blowing out some dark smoke. Not lots but a bit when it does start and then goes away once the engine settles into idle.

 

[GangsterOfLove]

A related question - what do these trucks use for a choke/fuel enrichment on cold starts?

What regulates it?

 

[Bstrom]

Might need to just give it a good once over in the maintenance department. Clean what can be cleaned -MAF, air filter, oil, etc. Then check out plugs, wires, coils, vacuum lines, fuel filter, fuel cap, etc. until all vitals are up to spec. Along the way you should/could find your main issue.

 

[duffbeer911]

bit of an update ... the mechanic changed some vacuum hoses, check the plugs and wires which were ok, but got to the fuel injectors and they were super dirty. Completely black and clogged. He soaked them in fuel (not sure if this is the right thing to do?!) and cleaned them but they still don't spray when connected to the battery and directly to some fuel ... it just sort of drips out. He connected an injector from another vehicle and it sprayed using the same testing method. Also blowing

So ... do you think this could be the cause of my problems? replace the fuel injectors or is there a better way to clean them? can I soak them in something?

thanks once again - appreciate the help!

 

[Arnezie]

This is who I've used in the past on my BMW http://www.witchhunter.com

 

[BamaDrewski]

This is who I've used in the past on my BMW WitchHunter Performance - Injector Cleaning & Flow Testing Services

It could be a couple of things. Clearly, from your post, the injectors are dirty.

You might check these two.

1. EFI Relay under hood in fuse block. (They should be "refreshed" with new ones every few years)
2. Run some fuel injector cleaner through your rig once a month.
3. BAD MILEAGE: For me - this equals 02 sensors - replace them. Amazon is the cheapest place I have found for the Denso's. On my non-California rig, (3.4L LTD 4WD) the fore and the aft O2's are the same part number: Denso 234-4162.
4. Definitely replace the fuel filter
5. ROUGH IDLE: Among the other things you mentioned, replace the TPS with an OE TPS.


Hope this helps man. With some TLC, your rig will live for a long, long time.

 

[Bstrom]

Might need to just give it a good once over in the maintenance department. Clean what can be cleaned -MAF, air filter, oil, etc. Then check out plugs, wires, coils, vacuum lines, fuel filter, fuel cap, etc. until all vitals are up to spec. Along the way you should/could find your main issue.

I've had a 'stumbly' starting experience off and on since I took ownership a couple weeks ago. Cleaned the MAF last week. It had new plugs just a few thou ago along with a new air filter. Had the battery and alternator checked today - they are OK. So I'm on to changing the fuel filter. Then if it continues I will check with the dealer again to see if plug wires were ever put on. Not gonna jump to conclusions. Fuel mileage if very good and driving is perfectly smooth so may just be a TB issue.

 

[4runnpdx]

Start by pulling your cats off and drive it around. See if it changes any things. if it does your cats may be clogged causing back pressure in your exhaust flow. Now if you do have clogged cats something had to have caused this so if your mechanic says your injectors are shot you may want to consider doing those as well.

 

[Ericsbr]

Coolant temp sensor?

 

[mmendelscfi]

I know the O2 sensors were already mentioned but I'll second that. We have a newer (2001) runner but had battled with inconsistent idle for a period of time. Every now and then would trip the CEL for the IAC valve, etc...... Then we tripped a CEL for the Air fuel sensor heating element.

We reset that but it would immediately trip again as I believe it means the element or circuit is completely open.

I believe the A/F sensor in the 2001 is the pre-cat O2 sensor in your model.

After replacing that the CEL for the AF sensor was gone but we also seemed to cure the poor idle and the IAC CEL we would sporadically get.

Bought it off Amazon. Hardest part of the job was removing what remained of the nuts off the studs that hold it on.

Thought I would pass this along.